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Phylogenetic relationships and infraspecificvariation in Canadian Arctic Poa based onchloroplast DNA restriction site data

Lynn J. Gillespie and Ruben Boles

Abstract: Infraspecific variation and phylogenetic relationships of Canadian Arctic species of the genusPoa were stud-ied based on chloroplast DNA (cpDNA) variation. Restriction site analysis of polymerase chain reaction amplifiedcpDNA was used to reexamine the status of infraspecific taxa, reconstruct phylogenetic relationships, and reexamineprevious classification systems and hypotheses of relationships. Infraspecific variation was detected in three species, butonly in Poa hartzii Gand. did it correspond to infraspecific taxa where recognition of subspeciesammophilaat the spe-cies level is supported. Additional variation inP. hartzii ssp.hartzii is hypothesized to be the result of hybridizationwith Poa glaucain the High Arctic and subsequent introgression resulting in repeated transfer ofP. glauca DNA. Thevariation in Poa pratensisL. had a geographical rather than taxonomic basis, and is hypothesized to correspond to in-digenous arctic versus introduced extra-arctic populations. InP. glaucaVahl cpDNA variation was detected only inwestern Low Arctic and boreal populations and may represent greater variation where the species survived the Pleisto-cene glaciations. Cladistic parsimony analysis of cpDNA restriction site data mostly confirms recent infrageneric classi-fication systems.Poa alpinaL., along with the non-arcticPoa annuaL. and Poa sect.Sylvestres, formed the basalmostclades. The remaining taxa group into two main clades: one consisting ofPoa sects.Poa, Homalopoa, MadropoaandDiocopoa; the second, ofPoa sects.Secundae, Pandemos, Abbreviataeand Stenopoa. Poa sect.Poa, comprisingPoaarctica R. Br. andP. pratensis, is a strongly supported monophyletic group, not closely related toP. alpina. Poa hartziiis confirmed as a member of a paraphyletic or weakly supportedP. sect.Secundae. Poa glaucaand Poa abbreviataR.Br. are distinct members within a generally unresolvedPoa. sect. Stenopoa–Abbreviataecomplex

Key words: Poa, Canadian arctic, chloroplast DNA, restriction site analysis, infraspecific variation, phylogeny.

Résumé: En se basant sur la variation de l’ADN chloroplastique, les auteurs ont étudié la variation infraspécifique etles relations phylogénétiques d’espèces du genrePoa de l’Arctique canadien. Il ont utilisé l’analyse des sites de restric-tion de l’ADN, amplifié par PCR, afin de réexaminer les systèmes de classifications antécédents et les hypothèses derelations. On décèle de la variation infraspécifique chez trois espèces, mais seulement chez lePoa hartzii correspond-elle à des taxons infraspécifiques où la reconnaissance de la sous-espèceammophilaest bien supportée. On formulel’hypothèse que la variation additionnelle repérée chez leP. hartzii subsp.hartzii résulterait de l’ hybridation avec lePoa glaucadans le haut-arctique et d’une introgression subséquente conduisant à un transfert répété de l’ADN de leP.glauca. La variation décelée chez lePoa pratensisa une base géographique plutôt que taxonomique et on proposel’hypothèse qu’elle correspond à des populations indigènes vs des populations extra-arctiques introduites. Chez leP.glauca,on ne décèle une variation du cpADN que chez les populations boréales et du bas arctique occidental, ce quipourrait représenter une variation plus importante là où les espèces ont survécu à la glaciation du Pléistocène.L’analyse cladistique en parcimonie, des données sur les sites de restriction du cpADN, confirment largement les systè-mes de classification infragénériques récents. LePoa alpina, avec lePoa annuaet lesPoa sect.Sylvestresnon-arctiques, forment les clades les plus fondamentaux. Les autres taxons se regroupent en deux clades principaux, uncomprenant lesPoa sects.Poa, Homalopoa, Madropoaet Diocopoa, et le second lesPoa sects.Secundae, Pendemos,Abbreviataeet Stenopa.Les Poa sect.Poa, comprenant leP. arctica et le P. pratensis, constituent un groupe monophy-létique fortement supporté, pas étroitement relié auP. alpina. Le P. hartzii se voit confirmé comme membre du groupe,paraphylétique ou faiblement supporté,Poa sect.Secundae. Le P. glaucaet le Poa abbreviataesont des membres dis-tincts à l’intérieur du complexe généralement irrésoluPoa sect.Stenopoa-Abbreviatae.

Mots clés: Poa, Arctique canadien, ADN chloroplastique, analyse des sites de restriction, variation infraspécifique,phylogénie.

[Traduit par la Rédaction] Gillespie and Boles 701

Can. J. Bot.79: 679–701 (2001) © 2001 NRC Canada

679

DOI: 10.1139/cjb-79-5-679

Received March 08, 2001. Published on the NRC Research Press Web site on June 6, 2001.

L.J. Gillespie1 and R. Boles.Research Division, Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, ON K1P 6P4,Canada.

1Corresponding author (e-mail: [email protected]).

J:\cjb\cjb79\cjb-06\B01-036.vpThursday, May 31, 2001 8:19:32 AM

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Introduction

The bluegrass genusPoaL. in the Canadian Arctic has beenstudied recently as part of floristic (McLachlan et al. 1989;Aiken et al. 1996a, 1996b) and taxonomic studies (Soreng1991b). This research, based on morphology, has highlightedareas of persisting taxonomic confusion that warrant furtherstudy. The present investigation uses restriction site analysis ofchloroplast DNA (cpDNA) amplified by polymerase chain re-action (PCR) to address these taxonomic problems and to studyphylogenetic relationships and biogeographic hypothesesamong Canadian Arctic species ofPoa. The genus is verywidespread in the Canadian Arctic, from sea level to close tothe upper altitudinal limit of vegetation, and as far north asnorthern Ellesmere Island. Species occupy a diversity of habi-tats, including densely vegetated mesic tundra, dry barrenslopes and ridges, sand plains and hills, and mesic and wetmossy meadows. Ecologically important as a component ofsuccessional vegetation, several species grow in naturally dis-turbed and often enriched sites such as riverbanks, erodingslopes, areas around animal burrows and remains, ancientdwelling sites, and recent human-disturbed sites.

With over 500 species,Poa is renowned to be a taxonomi-cally difficult genus. In North America alone the genus com-prises 71 species, 37 infraspecific taxa, and 3 named hybrids(Soreng and Kellogg 2001). Species are often difficult to de-fine and distinguish from closely related congeners. Highlevels of polyploidy, high incidence of asexual reproduction,and frequent occurrence of hybridization and introgressionare some of the factors believed to be responsible for thistaxonomic challenge (Clayton and Renvoize 1986; Kellogg1987). The paucity of clearly distinguishing, discrete mor-phological characters has led to a reliance on suites of over-lapping quantitative characters for identification, and, as aconsequence, unsatisfactory keys. Furthermore, many spe-cies ofPoaappear to vary morphologically depending on themicroenvironment; arctic species, in particular, have beendescribed as phenotypically plastic with broad ecologicaltolerances (Murray 1995).

Poa has been considered “an extremely uniform genus forwhich there is no satisfactory infrageneric classification”(Clayton and Renvoize 1986, p. 101). Classifications havebeen based primarily on morphological characters, and to alesser extent on ecological and cytological characters, mostlack a cladistic framework and, due to the size of the genus,are usually regionally based. We follow here the most recentinfrageneric classification ofPoa in North America (Soreng1998) that makes use of cpDNA restriction site data in acladistic framework in addition to morphology, ecology, andcytology. Other recent classifications pertaining to arctic andnorthern temperate species are also discussed (Edmondson1978, 1980; Tzvelev 1983).

Taxonomic history of Poa in the Canadian ArcticAlthough much of the Canadian Arctic flora has been

treated in several regional floristic studies, there has been nocomprehensive floristic treatment of the entire arctic regionof Canada, defined as the area north of the latitudinal tree-line. Outlined below is a brief taxonomic history ofPoa inthe Canadian Arctic.

The first floristic study of the entire Canadian Arctic Ar-chipelago treated eight species ofPoa and an additionalthree infraspecific taxa (Porsild 1957, 1964).Poa abbreviataR. Br., Poa arctica R. Br., Poa glaucaVahl, Poa hartziiGand., andPoa alpigenavar. colpodea(Th. Fr.) Schol. wereconsidered widespread in the Flora area;Poa arctica ssp.caespitans(Simm.) Nannf., andPoa arctica var. viviparaHook., as primarily eastern Arctic;Poa alpigenaLindm. andPoa alpinaL., as Low Arctic, reaching only the southernmostArctic islands; andPoa flexuosaSm. andPoa nascopieanaPolunin, with restricted distributions in the eastern Low Arc-tic. This work was partly based on previous regional floristicstudies of the Canadian Arctic Islands (Polunin 1940, 1955).

Five taxa ofPoa (P. abbreviata, P. alpigenavar. colpodea,P. arctica, P. glauca, and P. “×hartzii”) were included byMcLachlan et al. (1989) in their treatment of grasses of theQueen Elizabeth Islands, the northernmost island group. Thetwo infraspecific taxa ofP. arctica treated by Porsild (1957,1964), subspeciescaespitansand varietyvivipara, were bothsynonymized underP. arctica, whereasP. hartzii was treatedas a hybrid species. However, the status of each of thesethree taxa plus that ofP. alpigenavar. colpodeawas consid-ered to be uncertain. This study was expanded by Aiken etal. (1996a, 1996b) to cover all the Canadian Arctic Islands.In this study,P. hartzii was not formally treated as a hybridtaxon but was discussed as a possible hybrid, andP.alpigenavar. colpodeawas not considered distinct from theLow Arctic P. alpigena, which was treated here asPoapratensisssp.alpigena (Lindm.) Hiitonen. In addition, theLow Arctic speciesP. alpina was included, andP. arcticassp.caespitanswas treated as a distinct taxon following R.J.Soreng (herbarium annotations, 1990). The two additionalspecies mapped by Porsild (1957, 1964) as occurring onBaffin Island, P. flexuosa and P. nascopieana, were ex-cluded, as unconfirmed or of uncertain status, respectively.The authors remained uncertain of the status of many ofthese taxa and recommended that more detailed studies becarried out to resolve the persisting taxonomic uncertainties.

The mainland Canadian Arctic has been treated in largepart by Porsild and Cody (1980) and also by Cody (1996).In addition to the taxa treated above,Poa ammophilaA.E.Porsild is included as a locally common, N.W.T. endemicspecies, found primarily along the western arctic coast. Sev-eral alpine species are indicated as reaching the alpine–arctictransition zone of the northernmost cordilleras in the Yukonand westernmost N.W.T. but are not considered to be arcticspecies and will not be further discussed here. These includePoa abbreviatassp.pattersonii(Vasey) A. Löve, D. Löve &B.M. Kapoor (syn.Poa jordalii A.E. Porsild), Poa arcticassp. lanata (Scribn. & Merr.) Soreng (syn.Poa lanataScribn. & Merr.), Poa leptocomaTrin., Poa paucispiculaScribn. & Merr., andPoa pseudoabbreviataRoshev. Like-wise,Poa eminensJ. Presl, a seashore plant found primarilywithin the boreal ecozone, just reaches the Low Arctic innorthern Labrador and northwestern Quebec (Cayouette andDarbyshire 1993) and will also not be considered here.

Species ofPoa in the Canadian ArcticThe species ofPoa found in the Canadian Arctic are

described in detail below, including their distribution, taxo-

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nomic history, infraspecific taxa, and any systematic prob-lems or taxonomic uncertainties.

Poa abbreviataPoa abbreviatais an arctic–alpine circumpolar species

(although rare and with a very scattered distribution in east-ern arctic Russia), which was described from Melville Is-land. Of the three subspecies recognized in North America(Soreng 1991b), only P. abbreviatassp.abbreviatais foundin the Canadian Arctic. Considered to be a High Arctic cir-cumpolar taxon, this subspecies is primarily restricted to thearctic islands in Canada, with few known localities oncoastal mainland N.W.T. (Porsild and Cody 1980).Poaabbreviatassp.pattersonii, distinguished by the presence ofa well-developed web and shorter lemma pubescence, is pri-marily a North American Rocky Mountain alpine taxon,reaching the arctic only on Wrangel Island in Far EasternRussia (Tsvelev 1983 asP. abbreviata ssp. jordalii (A.E.Porsild) Hultèn; Soreng 1991b). Poa abbreviata ssp.abbreviata, the only subspecies to be considered here, ismorphologically distinct from other arctic taxa and nothighly variable. The species has been placed in its ownsmall, mainly Beringian section,Abbreviatae Nannf. exTzvelev, by all recent authors, although Tsvelev (1995) doessuggest that it is closely allied toP. sect.OreinosAsch. &Graebn.

Poa alpinaPoa alpina is an (sub)arctic–(sub)alpine species with an

interrupted circumpolar–circumboreal distribution (absentfrom most of arctic eastern Siberia). In the Canadian Arcticthe species is found in the eastern Low Arctic (easternBaffin Island, Southampton Island, northern Quebec, and theHudson Bay region), as well as in the subarctic across north-ern Canada and south in the western mountains to northernNew Mexico. Restricted to the Low Arctic and south inNorth America (primarily so in Greenland), in Eurasia itcommonly occurs in the High Arctic zone of Svalbard andon Novaya Zemlya. Canadian material was considered to behighly variable by Polunin (1940). Although consideringmost of this variation to consist of intergradating ecologicalforms, he did treat two varieties (P. alpina var. frigida(Gaudin) Rchb. andP. alpina var. bivonae(Parl. ex Guss.)St. John) and one forma (P. alpina f. brevifolia (Gaudin)Polunin). Subsequent authors have not considered anyinfraspecific taxa as occurring in the Canadian Arctic. Thespecies has been described as often viviparous (vivipary isused here in the sense of vegetative proliferation of florets),particularly in the eastern Canadian Arctic (Porsild 1957,1964; Porsild and Cody 1980). However, Polunin (1940)comments that no viviparous forms are found in this areaand Aiken et al. (1996a, 1996b) mention that plants withvegetatively proliferating inflorescences have not been col-lected in the Canadian Arctic Archipelago. Viviparous plantsare recognized as a distinct variety or subspecies in Green-land, Svalbard, and Russia (Böcher et al. 1968; Tzvelev1983, 1995; Rønning 1996) but generally not in NorthAmerica (Porsild 1957; Porsild and Cody 1980) and some-times not in Europe (Edmondson 1980).

Poa alpina has been classified in the following widelydivergent ways: inP. sect.BolbophorumAsch. & Graebn.

with the Eurasian Poa bulbosa L. species complex(Edmondson 1978, 1980; Tzvelev 1995); in its own section,Alpinae (Hegetschw. ex Nyman) Soreng, along with severalclosely related European species (Soreng 1998); and in itsown subsection,CaespitosaeV. Jirásek, in a broadly definedP. sect. Poa, which also includesPoa pratensis L., P.arctica, and P. bulbosa (Tzvelev 1983). Phylogenetically,the species has been considered closely related toP.pratensisand P. arctica (Nannfeldt 1940; Tzvelev 1983); tothe P. bulbosaspecies complex (Edmondson 1980; Tzvelev1983, 1995); or as the core species of a small isolated, earlydiverging species group, nearP. sect. Ochlopoa Asch. &Graebn. (Soreng 1990, 1998).

Poa arcticaPoa arcticais a widespread circumpolar arctic–alpine spe-

cies, considered to be highly polymorphic (Nannfeldt 1940;Edmondson 1980; Tzvelev 1983, 1995). In the CanadianArctic the species is currently considered to comprise twosubspecies based primarily on growth form and anther steril-ity (Aiken et al. 1996a, 1996b). Poa arcticassp.arctica isrhizomatous, with a dispersed or loosely turf-forminggrowth form, whileP. arctica ssp.caespitansis consideredto be caespitose or densely tufted, with rhizomes few andshort or absent, and apomictic with sterile pollen (Porsildand Cody 1980; Aiken et al. 1996b). Although their rangesoverlap considerably in the Canadian Arctic,P. arctica ssp.caespitansappears to be more common in the High Arcticand less so in the Low Arctic thanP. arctica ssp. arctica(Aiken et al. 1996b). Nannfeldt (1940) originally describedP. arctica ssp.caespitansfrom Ellesmere Island as a non-viviparous taxon with sterile anthers, but with viable seed,with a distribution from eastern Arctic Canada to Arctic Eu-rope and Novaya Zemlya. In the Russian Arctic,P. arcticassp. caespitansis treated as a separate species under thenamePoa tolmatchewiiRoshev. and is thought to be of prob-able hybrid origin withP. arctica and P. glauca as parentalspecies (Tzvelev 1983, 1995). Soreng and Kellogg (2001)also comment that the subspecies may be the result of hy-bridization between these two species. Rønning (1996) con-sidersP. arctica ssp.caespitansto be clearly distinguishablein Svalbard, whereas Edmondson (1980) describes a morebroadly definedP. arctica as a laxly caespitose, variable spe-cies and recognizes no infraspecific taxa in Europe. Recentstudies in Greenland have either treatedP. arctica ssp.caespitansas P. arctica var. caespitans(Simm.) Nannf.(Böcher et al. 1968) or not recognized it (Fredskild 1996),and R.J. Soreng (personal communication) considers a previ-ously recognized species,Poa filipes Lange (=trichopodaLange), to be clearly synonymous with the subspecies. Inaddition, Fredskild (1996) mentions thatP. arctica is diffi -cult to distinguish fromP. pratensisssp.alpigena in WestGreenland, where material is highly variable with numerousintermediates.

Poa arcticavar. vivipara was described from Somerset Is-land in Arctic Canada and is reported to occur sporadicallyaround the arctic. Polunin (1940) cited several collections,whereas Porsild (1957) and Porsild and Cody (1980)mapped the variety in 18 different localities in eastern ArcticCanada. Porsild (1955) had previously commented that theviviparous High Arctic Poa, which most previous authors

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had referred toP. pratensis or P. alpigena, seems bestplaced inP. arctica as var.vivipara but gave no specificreasons. More recently, Aiken et al. (1996a, 1996b) did notconsiderP. arctica var. vivipara to be a distinct taxon in theCanadian Arctic Islands, whereas Cody (1996) treated it asoccurring rarely in the Yukon from the arctic coast south to64°N. R.J. Soreng (personal communication), in a recentstudy of AlaskanPoa collections (ALA), found that vivipa-rousP. arctica specimens were restricted to alpine areas pri-marily south of 66°N. In the Russian arctic, the rarely foundP. arctica var. vivipara (Novaya Zemlya and the ChukoktaPeninsula) is considered to be a possible hybrid betweenP.arctica andP. pratensiss.l., and “is not always distinguish-able fromP. pratensisssp.colpodea” (Tzvelev 1983, p. 689,1995). The presence of viviparousP. arctica in the Cana-dian Arctic will be discussed in more detail in the Discus-sion.

Poa arctica is most often classified withP. pratensisplusa number of closely related Eurasian species inP. sect.Poa(Soreng 1998) or subsect.Poa (Tzvelev 1983). In contrast,Edmondson (1978, 1980) treatsP. arctica with the EuropeanPoa cenisiaAll. in P. sect. Cenisia Asch. & Graebn., re-stricting P. sect.Poa to the P. pratensiscomplex.

Poa glaucaPoa glauca, a common and widespread species in the Ca-

nadian Arctic, has a circumpolar, arctic–alpine distributionextending southward into the boreal zone. Among severalinfraspecific taxa recognized by Simmons (1906) as occur-ring on Ellesmere Island, varietytenuior Simmons was de-scribed based on slender, depauperate specimens fromEllesmere Island, but with the exception of a very tentativerecognition by Polunin (1940), none have been recognizedas distinct by subsequent authors. Subsequent to Simmons,botanists have been frustrated in their attempts to subdivideP. glauca in the Canadian Arctic and, for the most part, didnot; as Polunin (1940, p. 68) mentions “transitional formswere so abundant and the characters so unstable that the taskseemed futile.” Most recently, Soreng and Kellogg (2001)treat the western North American alpinePoa glaucassp.rupicola (Nash) W.A. Weber as a separate, but weakly de-marcated taxon, and Soreng (herbarium annotations, 1999)considers it to likely occur in the Canadian Arctic. Tzvelev(1983) recognizes three subspecies in Russia and considersP. glaucassp.glaucato be “highly polymorphic…, probablydivided into several still insufficiently studied taxa” (1983,p. 718). Tzvelev (1995) recognized numerous infraspecificand segregate taxa in Russia, of which two,Poa anadricaRoshev. andPoa bryophilaTrin. (treated as varieties ofP.glaucassp.glauca in Tzvelev 1983), were considered as ap-parently or probably occurring in the Canadian Arctic. How-ever, recent studies in Siberia argue against the subdivisionof P. glauca (Olonova 1993).

Poa glauca belongs to the primarily EurasianP. sect.StenopoaDumort. Tzvelev (1995, p. 212) considers this sec-tion to comprise numerous closely related species that aretied closely to one another by transitional populations, “... sothat under a broader species concept they might all be con-sidered subspecies of a single gigantic polytypic species(Poa nemoralisL. s.l.).” Poa glauca is considered to beclosely related toP. nemoralis, a species both native to and

widely introduced in North America and, according toTzvelev (1995), even more closely related to the SiberianspeciesPoa botryoides(Trin. ex Griseb.) Roshev. andPoastepposa(Krylov) Roshev. Intermediates betweenP. glaucaandP. nemoralisor Poa palustrisL. are common where thespecies are sympatric (Soreng and Kellogg 2001). In Green-land, forms that appear transitional withP. nemoralishavebeen treated asPoa glaucavar. glaucantha(Gaudin) Blytt(Böcher et al. 1968). Recent suggestions considered for theFlora of North Americawere the treatment ofP. glauca aseither synonymous with (proposed by E.A. Kellogg) or as asubspecies ofP. nemoralis(R.J. Soreng, personal communi-cation).

Poa hartziiPoa hartzii is an arctic species found sporadically from

Svalbard westward across arctic North America to WrangelIsland, with areas of greatest abundance in northeast Green-land and the Canadian High Arctic. A detailed account of itstaxonomic history and systematic problems is given inGillespie et al. (1997); only a brief summary will be pro-vided here. Two subspecies ofPoa hartziiare currently rec-ognized in the Canadian Arctic.Poa hartziissp.ammophila,endemic to the mainland N.W.T Beaufort Sea coast, wasoriginally described asP. ammophilaby Porsild (1943) andtreated as such by Porsild and Cody (1980) but was consid-ered to be included withinP. hartzii by Polunin (1959) andScoggan (1978) and as a subspecies by Soreng (1991b).Poahartzii ssp.hartzii is widespread but scattered on the ArcticIslands with one disjunct population on the arctic coast ofnorthern Quebec (Cayouette 1984) and two on the BeaufortSea coast of mainland N.W.T. (Soreng 1991b; Table 1,voucher Nos. 6397, 6398). Viviparous plants (i.e., with vege-tatively proliferating florets) ofP. hartzii ssp. hartzii werefirst collected from Ellesmere Island (Simmons 1906) andconsidered as a distinct variety, var.vivipara Polunin, orform, f. prolifera (Simmons) B. Boivin (based onP. glaucavar. atroviolaceaf. prolifera Simmons). AlthoughP. hartziif. prolifera was recognized by Boivin (1967) and Scoggan(1978), neither taxon was treated or discussed by otherauthors of Canadian Arctic floras (Porsild 1957, 1964;McLachlan et al. 1989; Aiken et al. 1996a, 1996b). Vivipa-rous plants have recently been collected from Axel Heiberg,Melville, and Victoria islands (herbarium specimens atCAN, Table 1, voucher Nos. 6623, 6624) and are found inpopulations comprised entirely of proliferating plants or,more frequently, mixed with non-proliferating plants. Out-side the Canadian Arctic viviparous plants are known fromGreenland where they are treated asP. hartzii f. prolifera(Bay 1993) and Wrangel Island, Russia, where they are con-sidered either as a distinct species,Poa vrangelicaTzvelev(Tzvelev 1983) or variety, P. hartzii var. vrangelica(Tzvelev) Prob. (Probatova 1984).

Poa hartzii ssp.hartzii has previously been suggested tobe a hybrid betweenP. abbreviataand eitherP. glaucaor P.arctica (Scholander 1934; Nannfeldt 1935; Edmondson1980). In our previous study investigating the role of hybrid-ization in the evolution of this species,P. hartzii ssp.hartziiwas determined to be a morphologically distinct apomictictaxon with two very different cpDNA haplotypes (Gillespieet al. 1997). The presence of these two haplotypes, deter-

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mined to be identical to theP. glauca and Poa secundaJ.Presl. species complex haplotypes, suggested that hybridiza-tion had been involved in its evolution. Two hypotheseswere formulated as a result of these findings. The first sug-gests thatP. hartzii is a stabilized intersectional hybrid be-tweenP. glauca and a species in theP. secundacomplex.The second hypothesis suggests that an ancestralP. hartzii,closely related toP. secunda, “captured”P. glauca cpDNAby hybridization and introgression.

Poa hartziiwas placed inP. sect.Abbreviataeby Tzvelev(1983) and, following him, by Soreng (1991a), consideredan apparently stabilized intersectional hybrid (probablybetween sects.Stenopoaand Abbreviatae) by Edmondson(1980) and most recently considered a member ofP. sect.SecundaeV. Marsh ex Soreng (Soreng 1991b; Soreng andKellogg 2001).

Poa pratensisThree taxa withinP. pratensisare currently recognized in

the Canadian Arctic.Poa pratensisssp. pratensis, a wide-spread temperate–boreal species thought to be introducedfrom Eurasia, reaches the arctic at several localities in north-ern Quebec (Porsild and Cody 1980) and along the mainlandBeaufort Sea coast (based on keys in Porsild and Cody1980; Cody 1996).Poa pratensisssp.alpigenais an indige-nous circumpolar arctic–alpine taxon. Although previouslytreated as the distinct speciesP. alpigena (Porsild 1957,1964; Porsild and Cody 1980; McLachlan et al. 1989), thetaxon has been most recently treated, in Canada, as a sub-species ofP. pratensis (Aiken et al. 1996a, 1996b; Cody1996) following Tzvelev (1983) and Soreng (1991b). In theCanadian Arctic,P. pratensisssp.alpigenais found primar-ily in the Low Arctic with scattered populations on PrincePatrick, Melville, Ellesmere (primarily on the Fosheim Pen-insula) and Axel Heiberg islands in the High Arctic.

The third taxon,Poa pratensisssp. colpodea (Th.Fr.)Tzvelev, was recognized asP. alpigena var. colpodeabyPorsild (1957, 1964), Porsild and Cody (1980), andMcLachlan et al. (1989), and asP. pratensisssp.alpigenavar. colpodeaby Soreng (1991b) but was not considered dis-tinct by Aiken et al. (1996a, 1996b). Tzvelev (1983) consid-ered the taxon asP. pratensisssp. colpodea, a treatmentfollowed by Edmondson (1980) and Soreng and Kellogg(2001). In Canada, this circumpolar taxon is primarily re-stricted to the Arctic Islands, with several coastal mainlandarctic populations (Porsild and Cody 1980). Soreng (1991b)considered the taxon to be a High Arctic small viviparousform of P. pratensisssp.alpigena, suggesting the possibilitythat vivipary may be a fixed or plastic response of the taxonto the extreme High Arctic environment. A second vivipa-rous form, P. pratensis ssp. alpigena var. vivipara(Malmgren) Schol., considered a distinct taxon in Svalbard(Rønning 1996), may occur on Ellesmere (based on twoSimmons collections recently examined at O) and Melville is-lands (based on recent field collections). Tzvelev (1995) com-ments that these two viviparous taxa are hardly distiguishableand considers most specimens of the latter taxon to likely bethe result of a hybrid cross betweenP. alpigena and P.arctica, a hypothesis also considered by Soreng (1991b) for P.pratensisssp.colpodea.

Soreng and Barrie (1999) consider theP. pratensiscom-plex to be extremely variable in morphology and cytologywith frequent asexual reproduction and discuss the history oftreating taxa in this complex as species versus subspecies orvarieties.Poa pratensis, the type species of the genus, isclassified in the mostly EurasianP. sect.Poa (subsect.Poa inTzvelev 1983).

Poa flexuosaand P. nascopieanaPoa flexuosa was considered by Porsild (1957) and

Porsild and Cody (1980) to occur on eastern Baffin Island,northern Labrador, and along the western shore of HudsonBay. The taxon was treated asPoa laxaHaenke ssp.flexuosa(Sm.) Hyl. by Scoggan (1978). In contrast, Aiken et al.(1996a, 1996b) excluded the taxon from the Arctic Islandflora as unconfirmed, whereas Soreng (1991b) consideredmost of the previously annotated collections to be referableto P. glauca s.l. The status of populations attributed toP.flexuosaby Porsild will not be addressed here but will be thefocus of a future study.

Polunin (1940) describedP. nascopieanabased on a sin-gle collection from the Pangnirtung area on Baffin Island.The species was treated by Porsild (1957, 1964) with oneadditional locality in the Clyde River area, Baffin Island, butwas excluded from the Arctic Archipelago flora by Aiken etal. (1996a, 1996b). These collections have abnormally de-veloped inflorescences making it difficult to be sure of theiridentity. R.J. Soreng (personal communication) considersthese collections to be most likeP. glauca in vegetative fea-tures and has recently recognized a third collection fromLake Hazen, Ellesmere Island (Murray & Yurtzev 10133ALA), that is similar to the type. The species remains an un-certain taxon, possibly synonymous withP. glauca, and willnot be further dealt with in this study.

Chloroplast DNA has been shown to be useful in definingplant taxa and to infer both infrageneric and infraspecific re-lationships (Palmer et al. 1988; Soltis et al. 1992, and refer-ences therein). In the genusPoa, Soreng (1990) successfullyused cpDNA restriction site variation, mapped for the wholecpDNA genome, to reconstruct phylogeny, provide an inde-pendent test of relationships inferred from morphologicaldata, and serve as markers of geographic radiation. Gillespieet al. (1997) determined PCR-amplified cpDNA restrictionsite data from two intergenic regions to be sufficiently vari-able within Canadian ArcticPoa to be useful in characteriz-ing species and also in detecting hybridization inP. hartzii.Although the need for greater taxon sampling has been dis-cussed previously (Soltis et al. 1992), most cpDNA phylo-genetic studies assume that infraspecific variation is absentor negligible and utilize a single individual to represent aspecies. The difficulties in adequately characterizing speciesand infraspecific taxa ofPoa based on morphology provideeven more reason to broadly survey genetic variation infra-specifically. In our previous study (Gillespie et al. 1997) wesurveyed for infraspecific variation prior to phylogenetic anal-ysis. Whereas the majority of arctic species were found to becharacterized by a single unique haplotype, infraspecificcpDNA variation was detected in High ArcticP. hartzii (acase involving hybridization) and Low ArcticP. glauca.

© 2001 NRC Canada




In the present study, restriction site analysis of PCR-amplified cpDNA is used to address problems of taxonomicstatus and to infer phylogenetic relationships in CanadianArctic Poa. This study expands on our previous study ofP.hartzii based on the variation found in two cpDNA regions(Gillespie et al. 1997). Three additional cpDNA regions areexamined here, and additional extra-arcticPoa species, out-groups, and collections of arctic taxa are evaluated.

In the first step of the study, infraspecific cpDNA varia-tion was surveyed within each arctic species, with the goalsof determining the presence and degree of such variation,elucidating the status of infraspecific taxa, and detecting hy-brid taxa. We were particularly interested in examining thestatus of subspecies inP. arctica, P. hartzii, andP. pratensis;investigating the possible hybrid origin of some of thesetaxa; and further elucidating the origin ofP. hartzii by test-ing the two hypotheses formulated in Gillespie et al. (1997).A secondary objective was to determine if sufficient infra-specific variation exists in the cpDNA regions examined tobe useful in phylogeographic studies, especially to detectareas of greater infraspecific genetic diversity that may pro-vide evidence for refugia where species survived the Pleisto-cene glaciations.

The second step involved reconstructing the phylogeneticrelationships of arcticPoa species taking into account thisinfraspecific variation. Our goals were to examine the evolu-tion of arctic species in the broader context of the genus andto provide a test of both traditional classification schemesand previous phylogenetic hypotheses. Specific questions ofinterest here include the phylogenetic position ofP. alpina,the relationship ofP. arctica to P. pratensis, and the statusand affinities ofP. glauca. Whereas the focus of this paper ison Canadian Arctic species, the phylogenetic analysis pre-sented includes a representative sample of north temperate,primarily North American, species ofPoa chosen to repre-sent the majority ofPoa sections. This phylogenetic ap-proach provides a useful framework for studying ageographically restricted group of species in the broadercontext of the evolution of the genus. Given the large sizeand taxonomic complexity ofPoa, it would be impractical asa first step to include all or most species and unwise to ana-lyze a taxonomic subdivision of the genus. The phylogenypresented here should be considered as a preliminary work-ing hypothesis and represents one step towards producing amore comprehensive hypothesis of phylogenetic relation-ships in the genusPoa.

Materials and methods

Taxa and populations sampledThe taxa and populations sampled are listed in Table 1.

Ten arctic taxa ofPoa, representing six species and an addi-tional four subspecies, were sampled. A total of 9–57 indi-viduals of each arctic species (with the exception ofP.alpina) were examined to cover the geographic range and themorphological variation found in the Canadian Arctic. Onlythree individuals ofP. alpina were sampled because of field-work limitations and since it is primarily a subarctic–alpinetaxon reaching the Low Arctic only in eastern Canada. Usingthe collections sampled in our previous study (Gillespie etal. 1997) as a starting point, we added collections initially to

increase the geographical coverage (particularly within thearctic but also from elsewhere in North America where ap-plicable). Subsequently, additional collections were addedfor arctic species in which infraspecific cpDNA variationwas detected. Our sampling strategy focused on covering abroad geographic range, rather than on extensive within pop-ulation sampling. Note that each voucher collection numberrepresents a single individual. Field work was undertaken inthe Canadian Arctic to obtain material for DNA analysis asoutlined in Gillespie et al. (1997) during the summers of1997 and 1999. Observations were also recorded on the dis-tribution, ecology, reproduction, and morphological varia-tion of plants in each population sampled. All arcticPoapreliminary identifications were made by the first author;these were then rechecked and, if necessary, redeterminedby R.J. Soreng (Smithsonian Institution).

Twenty-onePoa species from outside the arctic region,primarily from North America, were chosen to represent themorphological diversity found within north temperatePoaand to represent most major sections (Table 1). Many ofthese collections were provided by R.J. Soreng. The subge-neric classification followed here is that of Soreng (1998).

Also included in Table 1 are the six arctic genera used asoutgroups in the cladistic analysis.Arctagrostis Griseb.,Arctophila (Rupr.) Rupr. ex Andersson,Dupontia R.Br.,Puccinellia Parl., andPhippsia (Trin.) R. Br. belong to thesame tribe, Poeae, asPoa, whereasHierochloë R. Br. be-longs to tribe Aveneae Dumort. (following the system ofClayton and Renvoize 1986).Puccinellia has been used asan outgroup in previousPoa cpDNA analyses (Soreng 1990;Gillespie et al. 1997).Arctagrostis and Dupontia are sug-gested to be very closely related toPoa based on phylogen-etic analyses of subfamily Pooidae using cpDNA andmorphological data (Soreng et al. 1990; Soreng and Davis2000), whereasArctophilahas not previously been surveyed.

DNA extraction and PCR amplificationDNA was extracted from leaf tissue of individual plants

and subjected to RNAase following the methods outlined inGillespie et al. (1997). The extraction methods were varia-tions of Doyle and Doyle’s (1990) modification of the hexa-decyltrimethylammonium bromide (CTAB) total DNAextraction method of Saghai-Maroof et al. (1984). The pri-mary method used was one modified for extraction from 10–50 mg of silica-gel dried leaf tissue in 1.5-mL Eppendorftubes, which yielded ample DNA (10–90 ng/µL) for PCRamplification.

Five regions of the chloroplast genome located within thelarge single copy region were amplified via PCR. Three re-gions, trnF–trnV, trnV–trnL and trnH–trnK, are new to thisstudy, whereas two, trnT–trnF (Taberlet et al. 1991) andrbcL–ORF106 (Arnold et al. 1991), were examined in ourprevious study (Gillespie et al. 1997). The amplification re-action mix and program for these latter two regions were de-scribed in that study. Modifications made in this study are0.2 mM of each dNTP and an annealing temperature of57°C for the trnT–trnF region, 1µΜ of each primer, 0.2 mMof each dNTP, 20µL “Q” solution (Qiagen, Mississauga,Ont.), and 1 unit ofTaq DNA polymerase for the rbcL–ORF106 region.

© 2001 NRC Canada

684 Can. J. Bot. Vol. 79, 2001



© 2001 NRC Canada


Taxon Section ETU Population location Vouchers

Arctic taxa

Poa abbreviataR. Br. Abbreviatae abbreviata Ellesmere I., Lake Hazen, 81°49′N, 71°20′W 6028

Ellesmere I., Tanquary, 81°24′N, 76°53′W 5957, 5959*

Ellesmere I., Eureka, 80°00′N, 85°57′W 5724, 5731

Cornwallis I., Resolute Bay, 74°15′N, 94°50′W 5810, 5814, 5816*, 5818

Poa alpinaL. Alpinae alpina Baffin I., Iqaluit, 63°45′N, 68°31′W 5717, 5723

U.S.A., Colorado 6299*

Poa arcticaR. Br. ssp.arctica Poa arctica Ellesmere I., Lake Hazen, 81°49′N, 71°20′W 5781*

Ellesmere I., 79°44′N, 83°10′W (mound form) 6647*

Baffin I., Pond Inlet, 72°47′N, 77°00′W 6045, 6055

Baffin I., Arctic Bay, 73°02′N, 85°10′W 6062*, 6071*, 6072*

Baffin I., Iqaluit, 63°45′N, 68°31′W 5701, 5702*, 5705 5706,

5709

Victoria I., Cambridge Bay, 69°07′N,

105°03′W5830, 5842

NWT, Tuktoyuktuk, 69°26′N, 133°03′W 5941*

NWT, Mackenzie Delta, 69°28′N, 134°35′W 6435*

Poa arcticassp.caespitans

(Simm.) Nannf.

Poa caespitans Ellesmere I., Tanquary, 81°24′N, 76°53′W 5964

Baffin I., Arctic Bay, 73°02′N, 85°10′W 6068*, 6069*

Baffin I., Pond Inlet, 72°47′N, 77°00′W 6041*, 6044*

Baffin I., Iqaluit, 63°45′N, 68°31′W 5704, 5722


105°03′W5843

Poa glaucaVahl Stenopoa glauca1, glauca2, glauca3 Ellesmere I., Lake Hazen, 81°49′N, 71°20′W 6005 (1), 6006 (1), 6007

(1)

Ellesmere I., Tanquary, 81°24′N, 76°53′W 5963 (1)*

Ellesmere I., Ridge Lake, 79°56′N, 84°40′W 5802 (1), 5804 (1)*, 5805

(1)

Baffin I., Iqaluit, 63°45′N, 68°31′W 5700 (1), 5715 (1)

Baffin I., Ogac Lake, 62°50′N, 67°22′W 6755-1 (1)*


105°03′W5823 (1), 5831 (1), 5834

(1), 5841 (2)

NWT, Nicolson I., 69°53′N, 129°02′W 5863 (2), 5873 (1)*, 5877

(2)*

NWT, Cape Dalhousie, 70°14′N, 129°40′W 5913 (1)

NWT, Stanton, 69°48′N, 128°42′W 5897 (1)*

NWT, Kitigazuit, 69°21′N, 133°41′W 5931 (1)

NWT, MacKenzie Delta, 69°04′N, 134°17′W 6452 (1)*

NWT, Prelude Lake, 62°34′N, 113°55′W 6352 (3)*, 6353 (1)*

U.S.A., Colorado 6303 (1)*

Poa glauca× P. hartzii glaucaxhartzii Baffin I., Pond Inlet, 72°47′N, 77°00′W 6054*

Poa hartzii Gand. ssp.hartzii Secundae hartzii1, hartzii2 Ellesmere I., Lake Hazen, 81°49′N, 71°20′W 5771 (1), 5783 (1), 5997

(2), 6000 (1), 6016 (1),

6017 (1), 6020 (1),

6024 (1)

Ellesmere I., Tanquary, 81°24′N, 76°53′W 5740 (2), 5945 (2), 5952

(1), 5960 (2), 5988 (2),

5990 (2)

Ellesmere I., Eureka, 80°00′N, 85°57′W 5725 (1), 5738 (2), 5726

(1), 5729 (1)

Ellesmere I., Hot Weather Creek, 79°58′N,

84°26′W6130 (2)*, 6146 (2)*

Ellesmere I., Ridge Lake, 79°56′N, 84°40′W 5807 (2)

Axel Heiberg I., 80°33′N, 90°41′W (viviparous

population)

6623-1 (2)*, 6623-2 (2)*,

6623-3 (2)*,

Table 1. Taxa and populations ofPoa and outgroupsArctagrostis, Arctophila, Dupontia, Hierochloë, Phippsia, andPuccinellia sampledfor DNA analysis.



© 2001 NRC Canada

686 Can. J. Bot. Vol. 79, 2001


6623-4 (2)*, 6623-5(2)*, 6624-1 (2)*

Axel Heiberg I., Depot Point, 79°37′N,

86°30′WA91-036 (1)

Axel Heiberg I., Expedition Fiord, 79°24′N,

90°48′W6118 (1)*, 6121 (1)*, 6124

(1)*


105°03′W5824 (2)*, 5833 (2), 5835

(2), 5849 (2), 6319 (2)*,

6323 (2)*, 6333 (2)*,

6351 (2)*

NWT, Cape Dalhousie, 70°11′N, 129°41′W 6397 (2)*, 6398 (2)*

Poa hartzii ssp.ammophila

(A.E. Porsild) Soreng

Secundae ammophila1, ammophila2 NWT, Nicolson I., 69°53′N, 129°02′W 5851 (1), 5869 (1)*, 5870

(1), 5882 (1), 5883 (1)*,

5890 (1)*, 5892 (1)*

NWT, Cape Dalhousie, 70°14′N, 129°40′W 5908 (1), 5909 (2), 5910

(1)*, 5911 (1), 5912

(1)*, 5915 (1)*, 6403

(1)*, 6405 (1)*

NWT, Kitigazuit, 69°21′ , 133°41′W 5916 (1), 5921 (1), 5933

(1), 6448 (1)*, 6451

(1)*

Poa pratensisL. ssp.pratensis Poa pratensis1, pratensis2 Baffin I., Iqaluit, 63°45′N, 68°31′W 6701-1 (1)*

NWT, Nicolson I., 69°53′N, 129°02′W 5852 (1), 5866 (1)

NWT, Stanton, 69°48′N, 128°42′W 5901 (1)*

NWT, Inuvik, 68°21′N, 133°43′W 6358 (1)*

Quebec, Gaspé Pen. 6455 (2)*, 6458 (2)*



Poa pratensisssp.agassizensis

(B. Boivin & D. Löve) R.L.

Taylor & MacBryde

Poa agassizensis U.S.A., Colorado

U.S.A., New Mexico

6309*

S5805*

Poa pratensisssp.alpigena

(Lindm.) Hiitonen

Poa alpigena Ellesmere I., Ridge Lake, 79°56′N, 84°40′W

Baffin I., Apex, 63°43′N, 68°27′W


105°03′W

5801, 5803

6790-1*

5837

NWT, Nicolson I., 69°53′N, 129°02′W 5858, 5880

NWT, Kitigazuit, 69°21′N, 133°41′W 5927

Poa pratensisssp.colpodea

(Th. Fr.) Tzvelev

Poa colpodea Ellesmere I., Tanquary, 81°24′N, 76°53′W

Cornwallis I., Resolute Bay, 74°15′N, 94°50′W

5951

5820Baffin I., Pond Inlet, 72°47′N, 77°00′W 6043*

Extra-Arctic species

Poa annuaL. Ochlopoa annua1, annua2 Ontario 6284 (1)*

British Columbia 6285 (2)*, 6288 (1)*

Poa arachniferaTorrey Dioicopoa arachnifera U.S.A., Oklahoma S5801*

Poa arida Vasey Secundae arida U.S.A., Oklahoma S5802*

Poa autumnalisMuhl. ex Elliot Sylvestres autumnalis U.S.A., Maryland S4680*

Poa bulbosaL. Bolbophorum bulbosa U.S.A., Nevada S5814*

Poa chaixii Vill. Homalopoa chaixii Russia, St. Petersberg S4677*

Poa chambersiiSoreng Homalopoa chambersii U.S.A., Oregon S5858*

Poa compressaL. Stenopoa compressa NWT, Prelude Lake, 62°34′N, 113°55′W 6352*

U.S.A., Colorado 6289*

Poa cusickiiVasey ssp.cusickii Madropoa cusickii1, cusickii2 U.S.A., Nevada S5829 (1)*

U.S.A., Nevada (“hansenii form”) S5830 (2)*

Poa cuspidataNutt. Homalopoa cuspidata U.S.A., Maryland S4679*

Poa fendleriana(Steudel) Vasey Madropoa fendleriana1, fendleriana2 U.S.A., Colorado

U.S.A., Colorado

6292 (1)*

6302 (1)*


Table 1 (continued).



The trnF–trnV, trnV–rbcL, and trnH–trnK regions wereamplified using primers homologous to, respectively, por-tions of two transfer RNA genes trnF and trnV, portions ofthe transfer RNA gene trnV and the gene coding forribulose-1,5-bisphosphate carboxylase, and portions of trans-fer RNA genes trnH and trnK (Demesure et al. 1995;

Dumoulin-Lapègue et al. 1997). Amplification reactionswere performed in 100-µL volumes containing 0.5µM ofeach primer, 0.2 mM of each dNTP, 10µL reaction buffer,1.5 mM MgCl2 (contained in the reaction buffer), 0.5µL oftemplate DNA, and 1 unit ofTaq DNA polymerase. To fa-cilitate amplification, 20µL “Q” solution (Qiagen) and an

© 2001 NRC Canada



Poa macranthaVasey Madropoa macrantha U.S.A., Oregon S5861*

Poa napensisBeetle Secundae napensis U.S.A., California S2926a

Poa nemoralisL. Stenopoa nemoralis1, nemoralis2 U.S.A., Maryland S4682 (1)*

U.S.A., Oregon S5856 (2)*

Poa nervosa(Hook.) Vasey Homalopoa nervosa U.S.A., Oregon S5849*

Poa palustrisL. Stenopoa palustris Ontario 6461*

Poa secundaJ. Presl. ssp.

secunda

Secundae secunda1, secunda2 U.S.A., Washington (“canbyi” form) Native Plants Inc. acces-

sion POCO4247 (1)a*

U.S.A., Nevada S5813 (2)*

Poa secundassp. juncifolia

(Scribner) Soreng

Secundae juncifolia U.S.A., Colorado S5809*

U.S.A. (“ampla” form) Sharp Bros. Seed Co.a

U.S.A. (“nevadensis” form) Davis et al. s.n.a

Poa sylvestrisA. Gray Sylvestres sylvestris U.S.A., Maryland S4678*

Poa trivialis L. Pandemos trivialis U.S.A., Maryland S4681*

Poa wheeleriVasey Homalopoa wheeleri U.S.A., Nevada S5825*

Poa wolfii Scribner Sylvestres wolfii U.S.A., Missouri S5800*

Outgroup taxa

Arctagrostis latifolia (R.Br.)

Griseb.

Arctagrostis Axel Hieberg I., 79°56′N, 87°15′W 6586*, 6587*

Arctophila fulva (Trin.) Rupr. Arctophila Banks I., 73°46′N, 119°57′W A99-230*

Dupontia fisheriR.Br. Dupontia Axel Heiberg I., 79°56′N, 87°15′W 6589*

Baffin I., Iqaluit, 63°45′N, 68°31′W 6699*

Hierochloë paucifloraR.Br. Hierochloe Cornwallis I., Resolute Bay, 74°41′N, 94°50′W 6248*

Phippsia algida(Sol.) R.Br. Phippsia Devon I., Dundas Harbour, 74°31′N,

82°33.5′W6668-1*

Baffin I., Nanisivik, 73°02′N, 84°33′W 6253*

Puccinellia andersoniiSwallen =Puccangustata Ellesmere I., Lake Hazen, 81°49′N, 71°20′W 5790

Puccinellia angustata(R. Br.)

Rand. & Redfield

Puccangustata Ellesmere I., Lake Hazen, 81°49′N, 71°20′W

Ellesmere I., Eureka, 80°00′N, 85°57′W

5784 5786

5732 5733 6159


105°03′W5836

Puccinellia arctica(Hook.)

Fern. & Weath.

=Puccangustata Victoria I., Cambridge Bay, 69°07′N,

105°03′W5844

Puccinellia borealisSwallen =Puccangustata NWT, Mackenzie Delta, 69°04′N, 134°17′W 6453*

Puccinellia bruggemannii

Sorensen

=Puccangustata Cornwallis I., Resolute Bay, 74°15′N, 94°50′W 5813

Puccinellia phryganodes(Trin.)

Scribn. & Merr.

Puccphryganodes Victoria I., Cambridge Bay, 69°07′N,

105°03′W5850

Puccinellia poaceaSorensen =Puccangustata Ellesmere I., Tanquary, 81°24′N, 76°53′W 5744

Puccinellia vahliana(Liebm.)

Scribn. & Merr.

Puccvahliana Ellesmere I., Ridge Lake, 79°56′N, 84°40′W

Devon I., Dundas Harbour, 74°31′N,

82°33.5′W

5808

6682*

Baffin I., Iqaluit, 63°45′N, 68°31′W 6794-1*

Note: Canadian arctic species ofPoa are listed first, followed by extra-ArcticPoa species and outgroup taxa; within a taxon, populations are arrangedgeographically from north to south and east to west. The sectional classification followed here is that of Soreng (1998). Canadian Arctic Island populations arelocated in Nunavut; detailed locality information is given only for Nunavut and the Northwest Territories (NWT). Voucher numbers refer to collections made byGillespie (deposited at CAN); S.G. Aiken, prefixed with an “A” (CAN); and R.J. Soreng, prefixed with an “S” (US). Each voucher number represents an individualplant within the specified population; those with an asterisk are new to this study. Values in parentheses are the evolutionary taxonomic unit (ETU) designations inthose cases where a taxon has more than one ETU.

aDNA obtained from R.J. Soreng and cited in his cpDNA study (Soreng 1990).

Table 1 (concluded).



additional 0.5–1 mM MgCl2 were often added to the trnV–rbcL reaction. Reaction mixes were overlayed with two orthree drops of mineral oil. The amplification program for thefirst two regions consisted of an initial denaturation step of4 min at 94°C; 25 (trnF–trnV) or 35 cycles (trnV–rbcL) of45 s at 92°C, 45 s at 57°C, 4 min at 72°C; and a final exten-sion step of 10 min at 72°C. The program for the trnH–trnKregion consisted of the same initial and final steps and 30cycles of 45 s at 92°C, 45 s at 62°C, 2 min at 72°C. Lengthof the amplified products was estimated by comparison withknown marker DNA ladders in 1.1% agarose gels stainedwith ethidium bromide (Sambrook et al. 1989).

Restriction site analysisTwenty-five restriction endonuclease enzymes were used

in the initial screening for variable restriction fragment pat-terns. Twenty four of these enzymes, having four to six basepair recognition sequences, are listed in Gillespie et al.(1997). One additional enzyme,PvuII, with a six base pairrecognition sequence (Promega, Fisher, Ottawa), was used inthis study. The amplification products were digested withone to four units of each restriction enzyme for 2 h follow-ing the manufacturer’s specifications. Restriction fragmentswere separated by electrophoresis in agarose gels (Sambrooket al. 1989) ranging in concentration from 1.1 to 2.3%, de-pending on the length of the fragments. The gels stainedwith ethidium bromide were then photographed on an ultra-violet light source.

For the three cpDNA regions new to this study, trnF–trnV,trnV–rbcL and trnH–trnK, 10 DNA samples representing allarctic Poa species, including both haplotypes ofP. hartziiand three species ofPuccinellia, were digested with eachrestriction enzyme to screen for variable restriction sites.Likewise, the trnT–trnF and rbcL–ORF106 regions werescreened for thePvuII enzyme. In addition, the trnT–trnF re-gion was rescreened for several enzymes (EcoRI, NciI, RsaI)using 10 species (sixPoa species of which four were arctic,two Puccinellia species,Phippsia, and Hierochloë), whereinitial screening results were somewhat unclear and (or) in-sufficient species had been sampled.

Following determination of the restriction enzymes thatproduced variable restriction fragment patterns for eachcpDNA region, all collections new to this study were pro-cessed for each of these useful region–enzyme combina-tions. For collections previously studied (Gillespie et al.1997), a representative sample (three to six individuals) fromeach taxon was processed for the three new DNA regions.Where variation was detected within a taxon, the remainingcollections of that taxon were then processed for all region-enzyme combinations variable withinPoa. Unusual infra-taxon variation was rechecked by amplifying and digestingthe DNA a second and often a third time.

Restriction fragment patterns were interpreted in terms ofrestriction site presence (character state 1) versus absence(character state 0) (Dowling et al. 1990). The binary datamatrix (Table 2) was analyzed by cladistic parsimony meth-ods using the program PAUP* version 4.0 beta 5 for Win-dows (Swofford 1998). The heuristic search option was usedwith default settings, including a simple taxon addition se-quence and tree bisection–reconnection (TBR) branch swap-ping. Subsequently, analyses were performed using a

random taxon addition sequence and 100 replications.Characters were treated either as normal reversible (Fitchparsimony, all character transformations equally likely) or as“Dollo” characters (parallel restriction site gains not al-lowed). The outgroup taxaArctagrostis, Arctophila,Dupontia, Hierochloë, Phippsia, and Puccinellia were in-cluded in all analyses and used to root the cladograms a pos-teriori. Support for the cladistic relationships was assessedusing bootstrap analysis (Felsenstein 1985). Bootstrap analy-ses were performed with 100 replications using the heuristicsearch option and default settings.

Results

PCR product length variationAll five cpDNA regions showed at least some length vari-

ation among genera and species. Of these, only the trnF–trnV and the rbcL–ORF106 regions showed length variationamong species ofPoa that was large enough to have a pro-nounced effect on fragment patterns.

The trnF–trnV region amplified product was found to varyfrom approximately 3100 to 3350 base pairs (bp) in length.Among arctic species,P. arctica and P. pratensishad theshortest amplification product (-3100 bp); followed byP.abbreviata, P. glauca, P. hartzii, Arctagrostis, Arctophila,Dupontia, andHierochloë(-3180 bp); thenP. alpina (-3280bp); andPuccinellia and Phippsiawith the longest amplifi-cation product (-3350 bp).

The rbcL–ORF106 region amplified product varied inlength from 2250 bp forP. alpina to 2550 bp forP. arcticaand P. hartzii (haplotypes hartzii2 and ammophila) amongarctic species ofPoa (as previously described in Gillespie etal. 1997). The six outgroup genera had longer amplificationproducts at approximately 2700–2750 bp (this estimate issomewhat longer than previously described forPuccinellia).Two extra-arctic species ofPoa (P. annua and Poatrivialis L.) and one species ofPuccinellia (Pu. borealisSwallen) were not successfully amplified for this region, inaddition to the five species ofPuccinellia that we were un-able to amplify in our previous study. We suspect that muta-tions have occurred in one of the primers of these speciesthat block annealing.

The trnV–rbcL amplified product of species ofPoa andthe six outgroup genera varied only slightly between 3900and 4000 bp in length. The trnH–trnK region amplifiedproducts of all seven genera were between 1950 and 2000bp in length. TrnT–trnF length variation of arctic species ofPoa and Puccinellia has previously been described(Gillespie et al. 1997);Phippsia is similar in length toPuccinellia(-1750), whereas the other outgroup genera varybetween 1800 and 1850 bp in length.

Restriction site analysis

Restriction fragment patternsThe five cpDNA regions sampled for the presence of

restriction site variation comprise approximately 10% (-13 450bases) of the chloroplast genome. A total of 43 region–en-zyme combinations were found to have variable and inter-pretable restriction fragment patterns (Table 2). The threecpDNA regions new to this study provided 30 useful region–

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enzyme combinations, whereas rescreening of the trnT–trnFregion yielded an additional three enzymes (EcoRI, NciI,RsaI) for a total of eight for that region.

Interpreting restriction fragment patterns in terms of re-striction site presence versus absence was relatively straight-forward for the three cpDNA regions (trnT–trnF, trnV–rbcL,trnH–trnK) having minimal length variation. For the rbcL–ORF106 and trnF–trnV regions, it was necessary to take intoaccount amplification product length variation in the inter-pretation of fragment patterns. In this way, fragment patternvariation resulting from restriction site differences was dis-tinguished from the sometimes considerable pattern varia-tion because of length differences (e.g., fragment patternvariation resulting from digestion of trnF–trnV withHinfIwas determined to be due solely to length variation).

Differences in interpretation of restriction fragment pat-terns between our present study and the previous one(Gillespie et al. 1997) are outlined below. Fragment patternvariation resulting from digestion of the rbcL–ORF106 re-gion with MspI enzyme was previously coded as patternrather than site differences. In this study with additional pat-tern variation, we were able to interpret this variation interms of restriction sites. Upon closer examination of thetrnT–trnF patterns forP. alpina, a consistent pattern was no-ticed across several enzymes, which led us to hypothesizethat insertion–deletion events, rather than restriction site dif-ferences, were responsible for the somewhat different frag-ment patterns. Several characters previously consideredunique to P. alpina were deleted and other charactersrecoded. Following a recheck of the data,Poa secundassp.juncifolia (Scribner) Soreng was determined to have onlyone haplotype, contrary to the two recorded previously.

Restriction site variationCollections (corresponding to individual plants) within

each taxon were grouped according to their restriction siteprofile. Each group characterized by an identical haplotypewas considered as a separate evolutionary taxonomic unit(ETU). Table 1 provides a summary of the taxa, the ETUs,and the collections included within each ETU. The data ma-trix comprising 52 ETUs and 114 restriction site charactersis given in Table 2. Because six species ofPuccinellia (Pu.andersoniiSwallen,Pu. angustata(R. Br.) Rand & Redfield,Pu. arctica (Hook.) Fern. & Weath.,Pu. borealis, Pu.bruggemanniiSorensen, andPu. poaceaSorensen) had iden-tical haplotypes and also contained missing data for therbcL–ORF106 region, one ETU (Puccangustata) was used torepresent all six species.

The trnF–trnV region was found to be by far the mostvariable region for the taxa and enzymes sampled, with atotal of 51 variable and interpretable restriction sites (Ta-bles 2 and 3). Among the remaining regions, trnT–trnFyielded 20 variable restriction sites, trnV–rbcL yielded 18sites, the rbcL–ORF106 region 14 sites, whereas only 11variable sites were found within the trnH–trnK region.

The majority of taxa examined consisted of a single ETU;that is, all individuals examined had identical haplotypes.The following six arcticPoa taxa are represented by a singleETU: P. abbreviata, P. alpina, P. arctica ssp. arctica, P.arctica ssp. caespitans, P. pratensis ssp. alpigena and P.pratensisssp.colpodea. In contrast, restriction site variation

was detected in fourPoa taxa known from the arctic (P.glauca, P. hartzii ssp.ammophila, P. hartzii ssp.hartzii andP. pratensisssp.pratensis). Note that only arcticPoa taxawere sufficiently sampled to allow detection of infrataxonvariation. However, despite the poor sampling within extra-arcticPoa taxa, restriction site variation was detected in fiveof these taxa (P. annua, Poa cusickiiVasey ssp.cusickii,Poa fendleriana(Steudel) Vasey,P. nemoralis, Poa secundaJ. Presl. ssp.secunda). Restriction site variation among arc-tic taxa at the species and generic levels is given in more de-tail below.

Infraspecific variationInfraspecific variation in restriction sites was detected in

three arcticPoaspecies (Tables 1 and 2).Poa pratensiscom-prises two haplotypes differing in three restriction siteswithin the rbcL–ORF106 region. All arctic collections of thespecies (including all collections of P. pratensissspp.alpigenaandcolpodeaand only arctic collections ofP.pratensis ssp. pratensis) share the haplotype pratensis1,whereas the six extra-arctic collections examined (includingplants identified asPoa pratensisssp. agassiziensis(B.Boivin & D. Löve) R.L. Taylor & MacBride and extra-arcticcollections ofP. pratensisssp.pratensis) share the haplotypepratensis2.Poa glaucaalso exhibited within species restric-tion site variation. The haplotype glauca2, represented bythree collections from two western arctic populations, dif-fered in a single trnT–trnF restriction site from the dominanthaplotype (glauca1), which is found throughout the Cana-dian arctic and also from outside the arctic in the N.W.T.,and Colorado. A third unique haplotype was found in oneindividual from boreal N.W.T. (from the same population asan individual with the glauca1 haplotype) and differs fromglauca1 in four sites (the above trnT–trnF site, 2 trnF–trnV,and 1 trnV–rbcL sites).

Differences between the two haplotypes ofP. hartzii ssp.hartzii, as previously determined (Gillespie et al. 1997),were further emphasized here. An additional six restrictionsite differences were found, for a total of 15 sites, distributedacross all five cpDNA regions examined but with the great-est number, seven, found in the trnT–trnF region.Poa hartziissp. hartzii (hartzii2 haplotype) andP. hartzii ssp. ammo-phila were previously found to have identical haplotypes(Gillespie et al. 1997). New to this study are restriction sitedifferences between these twoP. hartzii subspecies and alow level of cpDNA variation withinP. hartzii ssp.ammo-phila. The dominant haplotype ofP. hartzii ssp.ammophila,ammophila1, was found to differ in one trnT–trnF site andfour trnF– trnV sites from hartzii2. Four of these restrictionsite differences are apomorphies unique to hartzii2. Theinfrasubspecific variation detected withinP. hartzii ssp.ammophilaconsisted of a single individual differing in onetrnF–trnV site from all other individuals examined. This re-striction site character state is shared with both haplotypesof P. hartzii ssp.hartzii.

Infrageneric and intergeneric variationA summary of the cpDNA variation characterizingPoa

andPuccinellia is provided in Table 3. Few sites were foundto be unique to each of the genera.Poa was defined by onlythree unique restriction sites, as wasPuccinellia (although

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trnT–trnFa rbcL–ORF106b trnF–trnVc trnV–rbcLd trnH–trnKe

10 20 30 40 50 60 70 80 90 100 110 114

arctica 0010101110 1000100111 1010010101 0110101110 0010011101 1000010110 0010011001 1001110010 0011011010 1111011000 0101000111 1000caespitans 0010101110 1000100111 1010010101 0110101110 0010011101 1000010110 0010011001 1001110010 0011011010 1111011000 0101000111 1000pratensis1 0010101110 1000100111 0010010100 0010101110 0010011101 1000010110 0010011001 1001110010 0011011010 1111011000 0101000111 1000pratensis2 0010101110 1000100111 1011010101 0010101110 0010011101 1000010110 0010011001 1001110010 0011011010 1111011000 0101000111 1000agassizensis 0010101110 1000100111 1011010101 0010101110 0010011101 1000010110 0010011001 1001110010 0011011010 1111011000 0101000111 1000alpigena 0010101110 1000100111 0010010100 0010101110 0010011101 1000010110 0010011001 1001110010 0011011010 1111011000 0101000111 1000colpodea 0010101110 1000100111 0010010100 0010101110 0010011101 1000010110 0010011001 1001110010 0011011010 1111011000 0101000111 1000arachnifera 0010101110 0100100111 0010010101 0100001110 0010011101 1000110110 0011011001 0001110010 0011010010 1111011000 1101000111 1000chaixii 0010101110 0100100111 1010010101 0100001110 0010011101 1000110110 0011011001 0001110010 0011010010 1111011000 1101000111 1000chambersii 0010101110 0100100111 0010010101 0100001110 0010011101 1000110110 0011011001 0001110010 0011010010 1111011000 1101000111 1000cusickii1 0010101110 0100100111 1010010101 0100001110 0010011101 1000110110 0011011001 0001110010 0011010010 1111011000 1101000111 1000cusickii2 0010101110 0100100111 0010010101 0100001110 0010011101 1000110110 0011011001 0001110010 0011010010 1111011000 1101000111 1000cuspidata 0010101110 0100100111 1010010101 0100001110 0010011101 1000110110 0011011001 0001110010 0011010010 1111011000 1101000110 1000fendleriana1 0010101110 0100100111 1010010101 0100001110 0010011101 1000110110 0011011001 0001110010 0011010010 1111011000 1101000111 1000fendleriana2 0010101110 0100100111 0010010101 0100001110 0010011101 1000110110 0011011001 0001110010 0011010010 1111011000 1101000111 1000macrantha 0010101110 0100000111 0010010101 0100001110 0000011101 1000110110 0011011001 0001110010 0011010010 1111011000 1101000111 1000nervosa 0010101110 0000100111 0010010101 0100001110 0010011101 1000110110 0011011001 0001110010 0011010010 1111011000 1101000111 1000wheeleri 0010101110 0100100111 0010010101 0100001110 0010011101 1000110110 1011011011 0001110010 0011010010 1111011000 1101000111 1000glauca1 1011101001 1100101110 0011000101 0100001110 0010011101 1001110110 0011011001 0101011010 0011010010 1011011000 0000000011 1000glauca2 1010101001 1100101110 0011000101 0100001110 0010011101 1001110110 0011011001 0101011010 0011010010 1011011000 0000000011 1000glauca3 1010101001 1100101110 0011010101 0100001110 0010011101 1001110110 0011011001 ?101111010 0011010010 1011011000 1000000011 1000glaucaxhartzii 1011101001 1100101110 0011000101 0100001110 0010011101 1001110110 0011011001 0101011010 0011010010 1011011000 0000000011 1000compressa 1010101001 1100101110 0011010101 0110001110 0010011101 1001110110 0011011001 0101111010 0011010010 1011011000 1000000011 1000nemoralis1 1010101001 1100101110 0011010101 0110001110 0010011101 1001110110 0011011001 0101111010 0011010010 1011011000 ?000000011 1000nemoralis2 1010101001 1100101110 0011010101 0110001110 0010011101 1001110110 0011011001 0101111010 0011010010 1011011000 1000000010 1000palustris 1010101001 1100101110 0011010101 0110001110 0010011101 1001110110 0011011001 0101111010 0011010010 1011011000 1000000011 1000abbreviata 1110101001 1100101110 0011010101 0110001110 0010011100 1001110110 0011011001 0101111010 0011010010 1011011000 1000000011 1000trivialis 0010101101 1100000111 ?????????? ????001110 0010011101 1000110110 0011011001 0101111010 1011010000 1011011000 1000000011 1000hartzii1 1011101001 1100101110 0011000101 0100001110 0010011101 1001110110 0011011001 0101011010 0011010010 1011011000 0000000011 1000hartzii2 0010101110 1100110111 0011010101 0110001110 0011011101 1001110010 0001011001 0101111010 0011010010 1011011000 1001000011 1000ammophila1 0010101110 1100100111 0011010101 0110001110 0010011100 1001110110 0011011001 0101111010 0011010010 1011011000 1001000011 1000ammophila2 0010101110 1100100111 0011010101 0110001110 0010011101 1001110110 0011011001 0101111010 0011010010 1011011000 1001000011 1000arida 0010101110 1100100111 0011010101 0110001110 0010011100 1001110110 0011011001 0101111010 0011010010 1011011000 1001000011 1000juncifolia 0010101110 1100100111 0011010101 0110001110 0010011101 1001110110 0011011001 0001111010 0011010010 1011011000 1001000011 1000napensis 0010101110 1100100111 0011010101 0110001110 0010011101 1001110110 0011011001 0001111010 0011010010 1011011000 1001000011 1000secunda1 0010101110 1100100111 0011010101 0110001110 0010011101 1001110110 0011011001 0001111010 0011010010 1011011000 1001000011 1000secunda2 0010101110 1100100111 0010010101 0110001110 0010011101 1001110110 0011011001 0001111010 0011010010 1011011000 1001000011 1000alpina 0000100010 0111100001 1010110100 0100010110 0010010100 1000110110 0111111000 0111110110 0011010010 1111111110 1001000011 1000bulbosa 0000100010 0111100001 1010110100 0100010110 0010010100 1000110110 0111111000 0111110110 0011010010 1111111110 1001000011 1000annua1 0000010010 0011100100 ?????????? ????001111 0010000101 1110110101 0010001000 0111110010 0010010010 1111111001 1001001011 1010annua2 0000010010 0011100100 ?????????? ????001111 0010000101 1110110101 0010001000 0111110010 0010010010 1111111001 1001001011 1000autumnalis 0000101010 1100100111 0010110101 1110001110 0010010101 1000110110 0011011001 0101100000 0000010010 1111111000 1001001011 0000sylvestris 0000101010 1100100111 0010110101 1110001110 0010010101 1000110110 0011011001 0101100000 0000010010 1111111000 1001001011 0000wolfii 0000101010 1100100111 1010110101 1110001110 0010010100 1000110110 0011011001 0101110000 0000010010 1111110000 1001101011 0000Phippsia 0000101010 1100000110 1100111111 1111001100 0000010010 0100001110 0010010100 0111111000 0000000100 0000111000 1011000001 0101Puccangustata 0000101010 1100000110 ?????????? ????001000 0000010010 0100001110 0010010100 0110101000 0000000100 0000101000 1011000001 0101Puccphryganodes 0000101010 1100000110 1110111111 1110001000 0000110010 0100001110 0010010100 0110101001 0000000100 0000101000 1011000001 0101Puccvahliana 0000101010 1100000110 1110111111 1110001000 0000010010 0100001110 0010010100 0110101000 0000000100 0000101000 1011010000 0101Arctagrostis 0000101010 1100100111 0111111101 1110001100 1110000101 1000110110 0011011000 0101111000 0100110010 1111111000 1001000010 0000Arctophila 0000100010 1100100111 0110111001 1110001100 1010000101 1000110110 0011011000 0101111000 0100110011 1111111000 1001000011 0010

Table 2. Data matrix of restriction site characters for eachPoa and outgroup evolutionary taxonomic unit.

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the Puccinellia + Phippsia group was characterized by 17unique sites). Since the remaining outgroups were not in-cluded in the initial screening for restriction fragment pat-tern variation, the number of restriction sites defining theseoutgroups is likely to be greatly underestimated, and as a re-sult, their relationships poorly resolved. For this reason theseoutgroups are not included in this comparison.

Sites variable withinPoa comprised, by far, the largestcategory, with 80 variable sites (of a total of 114), of which70 were cladistically informative (i.e., sites with gains orlosses that are shared by two or more ETUs). In sharp con-trast to this high degree of cpDNA variation inPoa is the ex-tremely low degree of variation found withinPuccinellia.Six of the eight arcticPuccinellia species sampled shareidentical haplotypes. OnlyPuccinellia phryganodes(Trin.)Scribn. & Merr. andPuccinellia vahliana(Liebm.) Scribn.& Merr. were found to differ by two and one unique sites,respectively.Puccinellia vahlianashares a single site withETUs outside of the genus (a parallel loss), but nocladistically informative sites are shared among species ofPuccinellia.

Cladistic analysis of restriction site dataThe data matrix used in the cladistic analysis comprises

52 ETUs and 114 restriction site characters (Table 2).Ninety-eight characters are cladistically informative, i.e.,shared by two or more ETUs, whereas 16 sites define singleETUs (Table 3). Data was scored as missing (?), signifying“state unknown,” for the following reasons: cpDNA regionwas not successfully amplified (rbcL–ORF106 region forfour ETUs), or interpretation of fragment patterns was am-biguous for a particular site because of length variation ofamplified product (trnF–trnV region). The eight outgroupETUs listed in Table 2 were included in all analyses. Notethat branch lengths are underestimated (sometimes consider-ably so) and relationships poorly resolved in outgroupclades, since the outgroup taxa, with the exception ofPucci-nellia, were not screened for variable restriction sites.

Parsimony analysis of this data matrix, with characterstreated as normal reversible (Fitch parsimony), resulted in asingle most parsimonious tree 157 steps in length with aconsistency index (CI) of 0.73 and a rescaled consistency in-dex (RC) of 0.68 (Fig. 1). Within the genusPoa, P. sect.SylvestresV. Marsh ex Soreng formed the basalmost clade,followed by a clade comprisingP. annua (sect.Ochlopoa)and P. alpina (sect. Alpinae) + P. bulbosa (sect. Bolbo-phorum). This latter clade has particularly long branchlengths compared with theP. sect.Sylvestresclade. The re-maining species group into two clades. The first comprisesP. sects.Poa, DioicopoaE. Desv.,HomalopoaDumort., andMadropoa Soreng. Within this clade,P. sect.Poa forms astrongly supported clade, whereas the other three sectionstogether form a weakly supported clade with no resolutionof the three sections. The second main clade is comprised ofP. sect.Secundaeforming a basal paraphyletic complex (i.e.,not defined by any shared restriction sites),P. trivialis (sect.Pandemos) and a clade comprisingP. sects.AbbreviataeandStenopoa.

Constraining restriction site gains as uniquely derived(Dollo parsimony) resulted in two most parsimonious trees171 steps long (CI = 0.67, RC = 0.65). Figure 2 illustrates

© 2001 NRC Canada


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692 Can. J. Bot. Vol. 79, 2001

only those parts of the cladogram that differ from the clado-gram described above (Fig. 1). The two Dollo trees differfrom each other only in the order of branching of taxa withinthe P. sect.Poa clade. Overall the cladograms produced bythe Fitch and Dollo parsimony analyses are very similar(Figs. 1 and 2). Apart from differences in the lengths ofbranches, they differ only in the branching order withinP. sect.Secundaeand in the uncertainty in branching order in theP.sect.Poa clade. TheP. napensisandP. secundaETUs form aclade in the Dollo analysis but not in the Fitch analysis.

Discussion

Variation among cpDNA regionsIn terms of numbers of variable and informative restric-

tion sites the trnF–trnV region was, by far, the most useful,whereas the trnH–trnK region was the least useful (Table 3).However, in addition to differences in number of sites, theremay also be a large difference in the information content ofeach region; one of the more evident examples of this con-cernsP. sect.Poa and the rbcL–ORF106 region. All varia-tion detected betweenP. arctica andP. pratensisand withinP. pratensiswas found only in this region. No differenceswere detected based on the other regions sampled nor wereany found in a previous study (Soreng 1990), which sampledthe entire cpDNA genome but with fewer enzymes. Variationin the rbcL–ORF106 region also accounted for the infra-specific variation detected inP. cusickii, P. fendleriana, andP. secunda. Two sites (Table 2, sites 21 and 24) were partic-ularly variable, and are perhaps more useful at the infra-specific level than above.

Differences between the phylogenetic analysis ofGillespie et al. (1997) and the one presented here are alsodue to the number of cpDNA regions sampled (the previousanalysis was based on a subset of the regions used here) andthe different information content of each region. For exam-ple, the strongly supported monophyly ofP. sect.Poa in thisanalysis was due to shared restricton sites in the trnF–trnV,trnV–rbcL, and trnH–trnK regions. In our previous study,which did not include these regions,P. sect.Poa was para-phyletic.

Chloroplast DNA variation

PoaversusPuccinelliaDespite the apparent morphological uniformity inPoa, the

genus is genetically diverse. The majority of species exam-ined could be distinguished readily by cpDNA restrictionsite characters and were characterized by unique cpDNAhaplotypes. Exceptions were primarily species pairs andcomplexes (e.g.,Poa sylvestresA. Gray andPoa autumnalisMuhl. ex Elliot; P. napensisandP. secunda) that belong inthe same section and are considered to be closely related.The clade comprisingP. sects.Homalopoa, Madropoa, andDioicopoawas particularly poorly resolved with members ofdifferent sections sometimes having identical haplotypes. Itmust be noted that extra-arctic species were not included inthe initial screening for variable fragment patterns, so re-screening with enzymes not used in the study may provideadditional sites. Soreng (1990) also determined the degree ofcpDNA variation inPoa to be high enough to adequately de-fine most taxa and resolve higher level phylogenetic rela-tionships. This study was also unable to resolve relationshipswithin the Homalopoa, Madropoa, andDioicopoa clade.

The very low level of cpDNA variation found in arcticPuccinellia is in sharp contrast to the relatively high levelfound in arcticPoa. The majority ofPuccinelliaspecies ex-amined share identical cpDNA haplotypes. Only two spe-cies, Pu. phryganodesand Pu. vahliana differed from thispattern, each differing in two sites, with only one of thesesites being potentially cladistically informative. These twospecies are also morphologically divergent from other arcticPuccinellia species (Consaul and Gillespie 2001);Pu.vahlianaoften has been treated in the primarily Asian genusColpodium Trin. (Porsild and Cody 1980; Tzvelev 1983),whereasPu. phryganodesis the only species to have a rhizo-matous habit. Choo et al. (1994), in a study that includedspecies representative of the morphological diversity withinPuccinellia, also found a low degree of restriction site varia-tion. While 15 restriction sites varied withinPuccinellia inthis study, only three were cladistically informative.

Why is there such a great difference in degree of cpDNAinfrageneric variation betweenPoa and Puccinellia? Onereason may be very different evolutionary histories. The ge-nus Puccinellia may have evolved and diversified muchmore recently thanPoa. Species ofPuccinellia in the Cana-dian Arctic and possibly also in North America are perhapsmuch more closely related to one another and form a singleor few clades, whereas Canadian Arctic and North AmericanPoa species belong to many different clades (and sections)and are much more representative of global generic diver-

trnT–trnF rbcL–ORF106 trnF–trnV trnV–rbcL trnH–trnK All regions examined

PCR product length (base pairs) 1750–1850 2250–2750 3100–3350 3900–4000 1950–2000-13 450Total no. of variable sites 20 14 51 18 11 114Total no. of informative sites 18 12 42 17 9 98Poa, no. of unique sites 0 2 1 0 0 3Poa, no. of variable sites 20 8 35 10 7 80Poa, no. of informative sites 18 8 29 9 6 70Puccinellia, no. of unique sites 0 0 2 1 0 3Puccinellia, no. of variable sites 0 0 2 0 2 4Puccinellia, no. of informative sites 0 0 0 0 1 1Puccinellia + Phippsia, no. of unique sites 0 1 7 6 3 17

Note: For Poa and Puccinellia, the number of unique sites defining the genus and the number of variable and cladistically informative sites within thegenus are given.

Table 3. Amplification product length, total number of variable restriction sites, and total number of cladistically informative sites (i.e.,shared by two or more ETUs) for the five cpDNA regions examined.



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sity. Alternatively, cpDNA may evolve at a much slowerrate inPuccinelliathanPoa. But it is unclear why this mightbe so, as the two genera share similar life-history character-istics, with the main difference being a preference for salinehabitats byPuccinellia.

Poa infraspecific variationThe finding of infraspecific variation in three of six arctic

Poa species examined and five of six extra-arcticPoa spe-cies (the latter represented by low sample sizes and includ-ing only those for which more than one individual wasexamined) corroborates Harris and Ingram’s (1991) finding

that infraspecific cpDNA variation is relatively common andnot rare as is often assumed. This finding would suggest thatphylogenetic studies at the genus level or below that usethese cpDNA regions or others having similar levels of vari-ation need to sample more than one individual per speciesfor adequate representation of a species.

Although infraspecific restriction site varation was detected,this variation generally did not correspond with recognizedsubspecies or varieties in either arctic or extra-arctic speciesof Poa. The exception to this isP. hartzii, in which the twosubspecies examined,ammophilaand hartzii, were distin-guished by five restriction sites (comparing the dominant

Fig. 1. Analysis of relationships inPoa based on cpDNA restriction site data showing the single most parsimonious tree (CI = 0.73,RC = 0.68) from the Fitch parsimony analysis. Tree is shown as a phylogram, with branch lengths proportional to the number of re-striction site changes. Bootstrap values of 50% and over are shown at the nodes. Sections ofPoa are given on the right.



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694 Can. J. Bot. Vol. 79, 2001

haplotypes ammophila1 and hartzii2). The restriction sitevariation detected inP. pratensisand P. secundadid notcorrespond to currently recognized subspecies. No variationwas found inP. arctica for which two subspecies were ex-amined, whereas variation was detected in several species,such asP. glauca, for which subspecies were either not rec-ognized or not examined.

Poa infraspecific (or infrasubspecific inP. hartzii) varia-tion often represented variation within a population. Multi-ple haplotypes were detected in three of six populations ofP.glauca, one of three populations ofP. hartzii ssp.ammophilaand three of eight populations ofP. hartzii ssp. hartzii(counting only those populations in which two or more indi-viduals were examined). Intrapopulation variation was alsodetected inP. annua, the only extra-arctic species for whichmore than one individual per population was examined. Thisvariation may be the result of multiple lineages originatingfrom a polymorphic ancestor, novel mutations within a pop-ulation, or hybridization and introgression of closely relatedtaxa (Harris and Ingram 1991). In the exceptional case ofP.hartzii ssp.hartzii, the variation appears to be the result ofhybridization and introgression of two distantly related taxa.

Poaphylogeny and sectional classificationIn general, there is reasonably close correspondance of

clades supported in the cladistic analyses presented here andthe sectional classification of Soreng (1998).Poa sects.Poaand Sylvestresare resolved as strongly supported andweakly supported clades, respectively, supporting the statusof each of them as distinct monophyletic groups.Poa annuaand P. trivialis, the only representatives examined ofP.sects.Ochlopoaand Pandemos, respectively, are fairly iso-lated taxa on long branches, suggesting that these sectionsare also distinct taxa.Poa sect. Secundaeappears as aparaphyletic complex basal to theStenopoa–Abbreviatae–Pandemosclade. Poa sects.Stenopoaand Abbreviataeto-gether form a strongly supported clade that is poorly re-solved internally. Likewise, Poa sects. Homalopoa,Diocopoa, andMadropoatogether form a clade, but with noresolution of the individual sections.Poa alpina and P.bulbosa, the only representatives ofPoa sects.Alpinae andBolbophorumexamined, respectively, were found to sharean identical cpDNA haplotype and formed a strongly sup-ported clade distinguished by numerous apomorphies. Spe-cific relationships of the arctic taxa and congruence with theclassifications of Soreng (1998) and others are discussed inthe following section.

Although our previous cladistic analysis of arcticPoa(Gillespie et al. 1997) involved fewer sites, taxa, and out-groups, there is much congruence between the two analyses.In both, P. alpina is the basalmost arctic taxon andP. sects.Stenopoa, Abbreviatae, andSecundaeform a clade with sect.Secundaebasal and paraphyletic. The main difference in-volvesP. sect.Poa, which was paraphyletic withP. pratensisand P. arctica as separate but consecutive branches in ourprevious study (branches separated by a single restrictionsite, which P. pratensis shared with the Stenopoa–Abbreviatae–Secundaeclade, but not with P. arctica).Adding more outgroups (particularly several that appear tobe more closely related toPoa thanPuccinellia), more taxa(such as those in theHomalopoa–Diocopoa–Madropoacom-plex) and examining additional cpDNA regions resulted in astrongly supported, monophyleticP. sect.Poa.

Our results are, in general, consistent with the results ofthe only other cladistic analysis of the genus, Soreng’s(1990) cpDNA restriction site study. Soreng’s (1998) sec-tional classification is based partly on the results of hiscpDNA cladistic analysis. Allowing for the very differentsets ofPoa taxa included, the overall structures of the result-ing cladograms are very similar in the two phylogeneticstudies. Both studies indicate thatP. alpina, P. annua, andP.sect. Sylvestresare basal taxa in the genus, withP. sect.Sylvestres(plus P. eminensof P. sgen.Arctopoa (Griseb.)Prob., unpublished data) as the basalmost clade. The remain-ing taxa group into two main clades, each having a similarstructure and constituent taxa (at least at the sectional level).Although relationships of specific species are generally notcomparable, because of the very different set of taxa used,our study did provide much better definition and resolutionof taxa withinP. sect.Poa. Unfortunately, because of the dif-ferent data collection methods, the cpDNA data from thestudy by Soreng (1990) cannot be combined with this study.

Arctic Poa species and their phylogenetic relationships

Poa abbreviataPoa abbreviatassp.abbreviatais characterized by a unique

Fig. 2. Analysis of relationships inPoa based on cpDNA restric-tion site data. Two most parsimonious trees (CI = 0.67, RC =0.65) from the Dollo parsimony analysis, showing only the twoclades that differ from the cladogram in Fig. 1. The two Dollotrees differ from each other only in theP. sect.Poa clade, asshown at top.



and invariant haplotype, which is consistent with its distinctmorphology and low level of morphological variation in theCanadian Arctic. Our data suggest a strong affinity with spe-cies inP. sect.Stenopoaand, although not inconsistent with,does not provide support for classification of the species in aseparate section,Abbreviatae. Relationships of taxa in theStenopoa–Abbreviataeclade (Figs. 1 and 2) are poorly re-solved in our analyses and additional data are needed to pro-vide resolution here. Other subspecies ofP. abbreviataplusadditional species of the primarily BeringianP. sect.Abbreviataeshould be examined. Soreng (1990) includedtwo different species ofP. sect.Abbreviataein his cpDNAstudy and similarly found both to be aligned withP. sect.Stenopoain an unresolved relationship. Soreng (1991a) alsocomments that the two sections are morphologically alliedand that intersectional hybrids are known.

Poa alpinaThe two very distant populations sampled (Baffin Island

and alpine Colorado) shared an identical cpDNA haplotype.More populations, including those from the subarctic, needto be examined for an understanding of infraspecific varia-tion. Poa alpina is the most phylogenetically basal and iso-lated of the arctic species, a finding consistent with Soreng’sstudy (1990). A phylogenetic position close toP. bulbosabut distant from all other species examined in this study isstrongly supported by our data. This is consistent withEdmondson’s (1978) classification, which groups the twospecies together inP. sect. Bolbophorum. In contrast,Tzvelev’s (1983) classification, which suggests a close rela-tionship withP. pratensisandP. arctica (see also Nannfeldt1940), in addition toP. bulbosa, is not supported by ourdata. SinceP. alpina andP. bulbosawere found to share anidentical cpDNA haplotype, Soreng’s (1998) classification ofthe two species in separate sections is also not supported. Inour analysis,P. alpina + P. bulbosa formed a strongly sup-ported clade with another basal but derived speciesP. annua(P.sect.Ochlopoa), whereas in Soreng’s (1990) analysisP. alpinaandP. annuaare separate, but successive basal branches.

Poa arcticaOur results suggest thatP. arctica is very closely related

to P. pratensis, differing in only two or three restriction sitesin the rbcL–ORF106 region. Together, they form a stronglysupported clade (six synapomorphic sites), supporting theirtraditional classification together inP. sect. Poa (Tzvelev1983 as subsect.Poa; Soreng 1998) and confirming previousmolecular evidence (Soreng 1990). These results do not sup-port the statement that “P. arctica shows only a very remoteaffinity to the groupP. pratensiss.l.” (Tzvelev 1995, p. 197).

The two subspecies ofP. arctica examined (arctica andcaespitans) were not differentiated in our study; all 18 indi-viduals examined share an identical cpDNA haplotype.Thus, we found no evidence forP. arctica ssp.caespitansasa distinct taxon nor as a hybrid betweenP. arctica and P.glauca. Recent field observations also do not support theconcept of two morphologically distinct subspecies in theCanadian Arctic. Regarding the main character (distinctlytufted versus rhizomatous habit) used to distinguish the twosubspecies, there appears to be a continuum in degree oftuftedness, with intermediate conditions common, such asloosely tufted with some short rhizomes. In addition, there

appears to be, at least, two very different types of denselytufted Poa in the Canadian Arctic. One type, generallytreated asP. arctica ssp.caespitans, comprises mostly ro-bust plants with broad flat leaves and often tall floweringculms generally found in mesic stony habitats, whereas asecond type comprises very low mound-forming plants withvery short culms and is characteristic of cold moist to wetmeadows at higher elevations (Table 1, voucher No. 6647).This suggests that, in the Canadian Arctic, plants having atufted growth form represent at least two different lineagesand not a single genetically distinct taxon.

Poa arctica is a highly polymorphic species in the Cana-dian Arctic. Since this variation is far from being discretemorphologically or geographically, we question the validityand utility of recognizing infraspecific taxa in this area.Much of this variation seems to be correlated with habitatand thus taxa, may perhaps be better described as differentecotypes.Poa arctica ssp. caespitansaccounts for only asmall part of this variation. We tend to agree with Polunin(1940) that there appears to be so much variation, and plantsvary “in such a mixed and baffling manner that I have givenup on sorting out the more obvious traits.” Further molecularstudies using more variable DNA regions are needed to de-termine whether the different morphological types ofP.arctica should be recognized as distinct taxa.

Reports concerning a viviparous rhizomatous form ofP.arctica in the Canadian Arctic may be mostly erroneous. Al-though Porsild and Cody (1980) mappedP. arctica var. vi-vipara in 18 different localities throughout the EasternArctic, we have not been able to verify any of these records.Upon examination of herbarium specimens at CAN andDAO, none were located at CAN, whereas the several speci-mens at DAO were redetermined asP. pratensis ssp.colpodea. Porsild (1955) previously commented that mostviviparous High ArcticPoaseem best placed inP. arctica asvar. vivipara but, unfortunately, provided no explanation. Itappears that he may have reidentified collections ofP.pratensisssp.colpodeaasP. arctica var. vivipara in his sub-sequent works (Porsild 1957; Porsild and Cody 1980). Basedon our examination of field and herbarium specimens,P.pratensisssp.colpodeaappears to be the common vivipa-rous rhizomatousPoa in the Canadian Arctic Islands andP.arctica var. vivipara is either rare or not a distinct taxon. OurcpDNA results of viviparous rhizomatousPoa (identified asP. pratensisssp.colpodea) having aP. pratensishaplotypeand not theP. arctica haplotype, so far, support this conclu-sion. One of the localities sampled, Pond Inlet, was indi-cated by Porsild and Cody (1980) as a locality forP. arcticavar. vivipara but notP. pratensisssp.colpodea. Interestingly,there also appears to have been some confusion between thetwo taxa in the Russian Arctic (Tzvelev 1983, 1995). Giventhat spikelets are typically incompletely developed in plantswith vegetatively proliferating inflorescences, one reason forthis confusion may be the lack of important spikelet charac-teristics often used to distinguish the two taxa. Additionalcollections of viviparous rhizomatousPoa should be ana-lyzed to adequately address this question.

Populations of viviparousP. arctica ssp.arctica have alsobeen found in coastal arctic Yukon. While these have beenreferred to asP. arctica var. vivipara (Cody 1996), theseplants are much more robust than what is typically referred

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to as that variety and most likely do not represent the sametaxon. Other viviparous Canadian ArcticP. arctica includecollections ofP. arctica ssp.caespitansfrom Baffin Islandthat developed vegetatively proliferating inflorescences un-der greenhouse conditions, but were not observed to be vi-viparous in the field.

Poa glaucaThree haplotypes were detected inP. glauca. The majority

of individuals examined, including those from boreal and al-pine areas in addition to the Arctic, had the same dominanthaplotype. A second very similar haplotype (glauca2) wasdetected only in the western Low Arctic, in two mixed popu-lations. A third haplotype (glauca3) was detected in a singleindividual from boreal N.W.T., and is intermediate betweenthe two main P. glauca haplotypes and those of theP.nemoralis, P. palustrisandPoa compressaL. complex. Thisindividual was identified asP. glauca ssp. glauca but be-longed to a heterogeneous population that included plantsidentified asP. glauca sspp.glauca, rupicola, and glaucatending towardsPoa nemoralisssp. interior (Rydb.) W.A.Weber (Soreng, herbarium annotations 1999). Its intermedi-ate haplotype may be the result of phylogenetic infraspecificvariation or, perhaps more likely, due to hybridization andintrogression with the sympatricP. palustrisor P. nemoralis.In contrast, a second individual examined from this popula-tion and identified asP. glauca ssp. rupicola was found tohave the dominantP. glauca haplotype. Additional borealand alpine collections ofP. glaucaneed to be examined for amore thorough investigation of infraspecific cpDNA varia-tion in P. glaucaand to determine whether the intermediateglauca3 haplotype occurs only in this population or is morewidespread.

No firm evidence of hybridization was detected inP.glaucaon the basis of our cpDNA results. Although the spe-cies is hypothesized to hybridize and introgress withP.hartzii ssp.hartzii (as discussed underP. hartzii), cpDNA ofthat taxon was not detected in individuals ofP. glauca.Therefore, introgression of cpDNA appears to be unidirec-tional from P. glauca to P. hartzii ssp.hartzii.

Poa glaucabelongs toP. sect.Stenopoa, which (togetherwith P. sect.Abbreviatae) is not well resolved in our analy-ses (Figs. 1 and 2). Most of the species examined have iden-tical or very similar cpDNA haplotypes. Interestingly,P.glauca appears to be the exception, with two very similarhaplotypes that differ considerably from other species (apartfrom the single glauca3 individual discussed above). Thesuggestion thatP. glauca should be treated as a subspeciesof the widespread Eurasian speciesP. nemoralis (as pro-posed in a recent draft manuscript forFlora of North Amer-ica; Soreng and Kellogg 2001) is not supported by our data.The two haplotypes of arcticP. glauca differ from those ofP. nemoralisin four to six restriction sites in three or four re-gions, a greater difference than between many currently rec-ognized species ofPoa.

Poa hartziiThe two subspecies ofP. hartzii examined, subspecies’

ammophila (the dominant ammophila1 haplotype) andhartzii (hartzii2 haplotype), differ in five restriction sites, ofwhich four are uniquely derived in ssp.hartzii. In compari-

son, many currently recognizedPoa species differ in onlyone or two sites from closely related species (e.g., most spe-cies in P. sect. Secundaeor the Homalopoa–Madropoa–Dioicopoaclade), whereas some species pairs or complexeswere found to share identical haplotypes, e.g.,P. autumnalisandP. sylvestris, P. napensisandP. secunda(secunda1 andjuncifolia haplotypes). This comparatively large restrictionsite difference betweenP. hartzii sspp. ammophila andhartzii suggests that they may be better recognized at thespecies level (following Porsild 1943; Porsild and Cody1980; Cody 1996). In contrast, examined viviparous individ-uals ofP. hartzii ssp.hartzii had the hartzii2 haplotype, thusproviding no evidence for their recognition as a separate tax-onomic entity.

The occurrence of both subspecies at Cape Dalhousie onthe mainland N.W.T. Beaufort Sea coast, which was sug-gested on the basis of morphological evidence (Soreng1991b), is verified by our restriction site study. This localityrepresents a western range extension forP. hartzii ssp.hartzii in North America and is one of only three known onthe Canadian Arctic mainland. Cape Dalhousie is also theonly site where cpDNA variation was detected inP. hartziissp.ammophila. The one restriction site difference found ina single individual is shared withP. hatrzii ssp. hartzii(along with mostPoa taxa), perhaps suggesting a low levelof hybridization and cpDNA exchange between the two sub-species (although this would infer an atypical mode ofcpDNA inheritance or gene exchange).

Soreng (1991b, p. 407) suggested thatP. hartzii ssp.ammophilamay prove “to be a hybrid betweenP. secundaand P. hartzii.” Poa hartzii ssp. ammophilahas a cpDNAhaplotype distinct from both putative parents, suggesting ei-ther that it is a distinct taxon not of recent hybrid origin orthat a taxon or population within theP. secundacomplex notyet examined is a parent. Based on our results the dominanthaplotype ofP. hartzii ssp.ammophilawas found to be iden-tical to Poa arida Vasey known from the Great Plains andCanadian Prairies. However, these two taxa are morphologi-cally quite distinct and have never been thought to be relatedpreviously. Interestingly,P. arida is itself hypothesized to bea stabilized hybrid betweenP. secunda and either P.pratensisor P. arctica (Soreng and Kellogg, in press). Addi-tional collections ofP. arida need to be examined, since thesingle individual examined is not morphologically typical ofthe species and may itself be the result of hybridization pos-sibly with P. secunda(identification by R.J. Soreng).

Two hypotheses concerning the origin ofP. hartzii ssp.hartzii were formulated by Gillespie et al. (1997) and out-lined in the introduction. These hypotheses were based onthe presence of two very different cpDNA haplotypes, oneidentical to a haplotype ofP. glauca, the other to taxa inP.sect.Secundae. The present study confirms that the hartzii1haplotype is identical to the dominant haplotype ofP.glauca. In contrast, the hartzii2 haplotype, although con-firmed as part of theP. sect.Secundaecomplex, was deter-mined to be a unique haplotype characterized by fouruniquely derived restriction sites. These results are consis-tent with the hypothesis ofP. hartzii ssp.hartzii as a preex-isting taxon that “captured” P. glauca cpDNA viahybridization and introgression. The alternate hypothesis ofP. hartzii ssp.hartzii as a stabilized intersectional hybrid be-

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696 Can. J. Bot. Vol. 79, 2001



tween P. glauca and a species inP. sect.Secundaeis notsupported. All northern Canadian taxa belonging toP. sect.Secundae, plus other more southerly species, were examinedin an attempt to determine a second parental species. Notaxon withinP. sect.Secundae, nor any other species exam-ined, was found to have a haplotype identical to or evenclosely resembling the hartzii2 haplotype. Thus the hartzii2haplotype was determined to be unique toP. hartzii ssp.hartzii, strongly suggesting that it is the original or ancestralhaplotype of that subspecies.

Furthermore, the hartzii2 haplotype was found in popula-tions in all three geographical regions sampled (High Arctic,Victoria Island, and mainland N.W.T.), whereas the hartzii1haplotype was detected only in High Arctic populations. Al-though P. hartzii ssp.hartzii and P. glauca co-occur in allthree regions, our cpDNA evidence suggests that hybridiza-tion and introgression resulting in the transfer ofP. glaucacpDNA to P. hartzii ssp.hartzii is taking place only in theHigh Arctic.

In the High Arctic both haplotypes ofP. hartzii ssp.hartziiappear to be equally frequent (15 versus 16 individuals) andwere found to co-occur in three of the four most extensivelysampled populations (four to eight individuals). However,there appears to be considerable variation in the presence ofhaplotypes and their frequency within a population. For ex-ample, seven of eight individuals at Lake Hazen had thehartzii1 haplotype, whereas only one of six individuals atTanquary had this haplotype. The occurrence and degree ofintrogression is hypothesized to be dependent on the pres-ence, proximity and size ofP. glauca populations toP.hartzii ssp.hartzii populations. Although their habitat pref-erences overlap considerably,P. glaucaappears to be absentfrom, or very sparse on, coarse sand or marine clay depositswhereP. hartzii ssp.hartzii often thrives. The latter occursmore commonly by itself at Tanquary, where these habitatsare much more common, than at Lake Hazen. Introgressionwas not detected in the most extensively sampled AxelHeiberg population, a coastal viviparous population growingon a sand substrate in the absence ofP. glauca. In contrast,only the glauca1 haplotype was detected in the other two,albeit poorly sampled, Axel Heiberg populations whereP.glauca was also present. Habitat differences might bethought to explain the lack of the hartzii1 haplotype in theLow Arctic populations sampled. However, this is not thecase, sinceP. glaucaindividuals were found growing with ornear P. hartzii ssp.hartzii in both Low Arctic populationssampled.

The geographical distribution of the hartzii1 haplotypedescribed above suggests multiple recent hybridization andintrogression events in the High Arctic. In stabilized intro-gressed populations, one haplotype is thought to eventuallydominate becoming the only haplotype in the population orspecies (Reiseberg and Soltis 1991). The presence of boththe original and introgressed haplotypes throughout the HighArctic and in three of the four most extensively sampledpopulations suggests populations that have not stabilizedwith recent and perhaps continuing introgression. The pres-ence of putative hybrids that appear to be morphologicallyintermediate betweenP. hartzii ssp. hartzii and P. glaucaalso suggests that these events are recent and ongoing. Al-though rare, these hybrids have been collected recently at

several different localities; the one examined here wasdetermined to have the glauca1 haplotype. Although recent,ongoing introgression is the most likely explanation, an al-ternative possibility is stabilized introgressed populationshaving two codominant haplotypes that have reached a stateof equilibrium.

The above hypothesis is complicated by the fact thatP.hartzii ssp.hartzii appears to be apomictic with sterile pol-len (Soreng 1991b, Gillespie et al. 1997). If this taxon occa-sionally bears fertile pollen, then it could act as the pollendonor in the initial hybridization event, withP. glaucaactingas the maternal parent and plastid donor. On the other hand,if P. hartzii ssp. hartzii never bears fertile pollen, thenP.glauca would be both the pollen donor and plastid donor,which would imply a paternal or biparental mode of plastidinheritance (modes of inheritance reviewed for angiospermsby Harris and Ingram (1991)). Introgression via backcross-ing of the hybrid withP. hartzii ssp.hartzii, likewise, wouldimply either the latter as the pollen donor (and the hybrid asthe plastid donor) or the hybrid as both the pollen andplastid donor.

Counterfeit hybridization may provide an alternative ex-planation of cpDNA exchange betweenP. hartzii ssp.hartziiandP. glauca. In this gene transfer process, chromosomallynonreduced eggs are stimulated to develop parthenogeneti-cally by pollen of another species (pseudogamy), and al-though normal transfer of chromosomes from pollen to eggdoes not take place, gene transfer can occur (de Wet et al.1984; de Wet 1986). As previously described in Gillespie etal. (1997), pollen ofP. glauca may stimulateP. hartzii ssp.hartzii ovules to develop (pseudogamy). If this process isleaky and some cpDNA transfer occurs, thenP. glaucacpDNA could be introduced intoP. hartzii ssp. hartzii di-rectly via counterfeit hybridization, without the need for theintermediate step of true F1 hybrids followed by subsequentbackcrossing.

Poa pratensisPoa pratensishas infraspecific cpDNA variation with a

distinct geographical pattern. Restriction site data separatescollections examined into two groups, an arctic complex ofP. pratensiscomprising subspecies’alpigena, colpodeaandarctic individuals of subspeciespratensis, and a non-arcticcomplex comprisingP. pratensisssp.agassiziensisand non-arctic individuals of subspeciespratensis. The two cpDNAgroups, each characterized by a unique haplotype, differ inthree restriction sites. This level of variation is greater thanthat found within other species complexes or between manyspecies pairs ofPoa. We hypothesize that the two cpDNAgroups may represent a fundamental division between an in-digenous arctic complex and a primarily or entirely intro-duced non-arctic complex.

The cpDNA variation detected inP. pratensisdoes notcorrespond to the subspecific classification as currently ac-cepted. Individuals identified asP. pratensisssp. pratensishad one of two haplotypes depending on whether they werearctic or extra-arctic. This may reflect our poor understand-ing of subspecies boundaries rather than being real infra-subspecific variation. Arctic individuals keyed out asP.pratensis ssp. pratensis lacked features generally used tocharacterizeP. pratensisssp.alpigena, such as hairs on me-

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dial nerves of lemma (Porsild and Cody 1980) and only twobranches at the lowest node of the panicle (Edmondson1980; Cody 1996; Soreng and Barrie 1999). However, uponcloser examination these individuals were found to be inter-mediate in overall morphology between the two subspecies.All are from the Low Arctic and mostly from sites havingvarying degrees of human disturbance. Based on our cpDNAresults these individuals are likely indigenous and mostclosely allied withP. pratensisssp.alpigena. They may bethe result of hybridization of the two subspecies with thecpDNA of the nativeP. pratensisssp.alpigenadominating.

The two arctic subspecies examined,P. pratensissspp.alpigena and colpodea, share an identical haplotype,suggesting a close relationship but providing no evidencesupporting the recognition of the latter as a distinct subspe-cies. Although cpDNA of the viviparous form ofP. pratensisssp.alpigenawas not examined, recent observations on Mel-ville Island suggest that vivipary in this subspecies may beenvironmentally induced and thatP. pratensis subsp.alpigenavar. vivipara is likely not a distinct taxon in arcticCanada. Culms with vegetatively proliferating florets werealways found growing within patches of non-viviparousP.pratensisssp.alpigenaand, whenever the delicate rhizomeswere successfully excavated, they were found attached to thesame rhizome as non-viviparous culms (e.g., Gillespie &Consaul specimen No. 6942).

In North America extra-arcticP. pratensishas generallybeen treated underP. pratensisssp. pratensis, but Sorengand Kellogg (2001) consider these populations to representseveral European taxa (subspecies’angustifoliaand irrigata,in addition to subspeciespratensis), a complex of cultivarsproduced mostly in North America putatively from Euro-pean stock (primarily subspeciespratensis) and a putativenative taxon. The latter taxon,P. pratensisssp.agassizensis,was only recognized in 1960 from Manitoba (Boivin andLöve 1960). Individuals identified as this subspecies share ahaplotype with extra-arcticP. pratensisssp.pratensis. Thispoorly understood subspecies, although perhaps once a ge-netically distinct native form, may now be swamped with thecpDNA from widespread and pervasive introduced formsand cultivars.

Interestingly, extra-arcticP. pratensisshares more restric-tion sites withP. arctica than with arcticP. pratensis. Allrestriction sites distinguishing these three haplotypes are lo-cated in one cpDNA region examined, rbcL–ORF106. Threerestriction site losses distinguish arctic from extra-arcticP.pratensis. In addition, the length of the rbcL–ORF106 regionin arctic P. pratensiswas found to be distinctly shorter thanin both extra-arcticP. pratensisandP. arctica. The latter twohaplotypes have a similar PCR product length and differfrom each other in only two restriction sites. Given this sig-nificant length difference, the restriction site losses may bethe result of an insertion–deletion event, specifically a dele-tion in arcticP. pratensis, rather than the result of base sub-stitutions.

Poa pratensisin North America is considered to be a largepolymorphic complex of native, introduced, and cultivatedforms that are questionably distinguishable (Soreng andKellogg 2001; also cf. Soreng and Barrie 1999). The speciescomprises numerous facultatively apomictic and pseudo-gamous races, having varying degrees of apomixis and pol-

len fertility (Muntzing 1933; Bashaw and Hanna 1990).Kellogg (1987) describes this species (andP. secunda, an-other difficult species complex) as often appearing to com-prise distinct taxonomic units at a local scale but withboundaries that blur at a broader scale. The ability to hybrid-ize with other, sometimes distantly related species ofPoafurther complicates the picture (Soreng and Kellogg 2001).Given this evolutionary complexity the detection of geneticmarkers distinguishing two groups in North America is aninteresting finding and is currently being explored further.

Our results are consistent with a classification treatingP.pratensisin a section together withP. arctica but separatefrom any other species examined here, as discussed underthe headingPoa arcticaabove.

Biogeography and Pleistocene survivalPhylogeographic studies involving the examination of

geographic variation in infraspecific genetic diversity havebeen used to detect areas of greater genetic diversity thatmay provide evidence of where species survived the Pleisto-cene glaciations (Tremblay and Schoen 1999; Abbott et al.2000). Although our analysis of cpDNA variation did notdetect extensive infraspecific variation nor was it an in depthphylogeographic study, several of our results are interestingfrom a biogeographic perspective. InP. glauca, infraspecificvariation was detected in the western Low Arctic, but notfrom the High Arctic or eastern Low Arctic, suggesting thatCanadian Arctic populations may derive from populationsthat survived the Pleistocene glaciation in a Beringian re-fugium. More extensive sampling, particularly of easternLow Arctic, boreal and alpine populations is needed to testthis hypothesis. In general, however, cpDNA restriction sitedata detected insufficient infraspecific variation in arcticPoafor phylogeographic studies and other methods of DNAanalysis are needed for such studies.

Our cpDNA results provide further insight into the bio-geography ofP. hartzii and the evolution of its subspecies asdiscussed previously in Gillespie et al. (1997).Poa hartziisspp.hartzii and ammophila(and the Alaskan endemic ssp.alaskanaSoreng) were hypothesized to have originated byrange fragementation and isolation in widely separatedrefugia during the Pleistocene. In this scenario the westernArctic P. hartzii sspp.ammophilaandalaskanadiverged fol-lowing isolation in Beringian refugia, whereas the primarilyHigh Arctic P. hartzii ssp.hartzii likely originated in HighArctic refugia. Given the restricted geographical distributionof the P. glauca haplotype inP. hartzii ssp.hartzii, hybrid-ization and introgression appears to have played a later rolein the evolution of this subspecies. An alternative hypothesissuggested by their very distinct haplotypes is thatP. hartziisspp.ammophilaandhartzii are not most closely related anddiverged prior to the Pleistocene.

Conclusions

Restriction site analysis of specific cpDNA PCR productswas found to be a useful method for examining both speciesdelimitation and phylogeny in the genusPoa. Extensivewithin-species sampling of Canadian Arctic species was de-termined to be both informative and necessary to understandspecies delimitation and in detecting hybridization. Arctic

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species were, in general, characterized by one or moreunique cpDNA haplotype(s). Although infraspecific cpDNAvariation was detected in three arctic species, it corre-sponded to subspecific taxa in only one species.Poa hartziisspp. hartzii and ammophila were each characterized byunique haplotypes that are as or more different than manyclosely related species, suggesting recognition at the specieslevel. In contrast, the variation detected inP. pratensishad ageographic rather than taxonomic basis and is hypothesizedto correspond to indigenous arctic versus introduced non-arctic populations. Variation inP. glaucawas detected onlywithin western Low Arctic and subarctic populations andmay be an historical consequence of greater genetic diver-sity where the arctic populations survived the Pleistoceneglaciations. Our cpDNA analysis did not detect infraspecificvariation inP. arctica and was, therefore, not informative inexamining the status or possible hybrid origin of its infra-specific taxa.

The results of our expanded cpDNA study are consistentwith one of the two hypotheses concerning the evolution ofP. hartzii outlined in Gillespie et al. (1997). Populations ofP. hartzii ssp.hartzii were determined to contain two verydifferent haplotypes, one identical toP. glauca and the sec-ond a unique haplotype withinP. sect. Secundae. This isconsistent with the hypothesis ofP. hartzii ssp.hartzii as apreexisting taxon that has capturedP. glaucacpDNA via hy-bridization and introgression. Given that theP. glaucahaplotype was found only in High Arctic populations, hy-bridization appears to be taking place only in this region. Noindividuals of P. glauca were found to have theP. hartziissp.hartzii haplotype, suggesting that introgression is unidi-rectional, fromP. glauca to P. hartzii ssp.hartzii.

The phylogenetic analysis presented here of CanadianArctic and selected extra-arctic species is, in general, consis-tent with recent phylogenetic analyses and infrageneric clas-sification systems.Poa sect.Sylvestreswas determined to bethe most plesiomorphic of the taxa examined, whereasP.alpina, P. bulbosa, and P. annuaare basal but derived spe-cies. All remaining species examined grouped into two mainclades, one comprisingP. sects.Poa, Homalopoa, Madro-poa, and Dioicopoa, and the second composed ofP. sects.Secundae, Pandemos, Abbreviatae, and Stenopoa. PoaglaucaandP. abbreviatawere each found to be distinct taxawith characteristic cpDNA haplotypes within a generally un-resolvedP. sect.Stenopoa–Abbreviataecomplex.Poa hartziiis confirmed as belonging toP. sect. Secundae. Poa sect.Poa, consisting ofP. arctica and P. pratensis, is a stronglysupported monophyletic group, not closely related toP.alpina. Where previous phylogenetic hypotheses or classifi-cations differ, our results were often informative in provid-ing support for a particular hypothesis.

Two additional collections ofPoa alpinawere examined(Gillespie et al. 6749-1 from Ogac Lake, Baffin Island, andDjan-Chekar 00-126 from Newfoundland). Both collectionshave the alpina haplotype, identical to the three collectionsof P. Alpina that were examined in this study.

Acknowledgements

We gratefully acknowledge the field support provided tous by the staff at Polar Continental Shelf Project (PCSP),

Aurora Research Institute, Nunavut Research Institute, andEllesmere Island National Park. We especially thank RobSoreng for stimulating discussions, providing DNA of extra-arctic species and determiningPoa collections. LaurieConsaul, Rob Soreng, Claus Vogel, and FrançoiseChatenoud are gratefully acknowledged for their enthusiasticassistance in the field and Tina Saffioti, Izabella Szymanska,and John Coltess for their assistance in the laboratory. Re-search was funded by grants from the Canadian Museum ofNature and PCSP grants from the Canadian Museum of Na-ture and PCSP. This paper is Polar Continental Shelf ProjectContribution number 008-01.

References

Abbott, R.J., Smith, L.C., Milne, R.I., Crawford, R.M.M., Wolff, K.,and Balfour, J. 2000. Molecular analysis of plant migration andrefugia in the Arctic. Science (Washington, D.C.),289: 1343–1346.

Aiken, S.G., Consaul, L.L., and Dallwitz, M.J. 1996a. Grasses ofthe Canadian Arctic Archipelago: a Delta database for interac-tive identification and illustrated information retrieval. Can. J.Bot. 74: 1812–1825.

Aiken, S.G., Consaul, L.L., and Dallwitz, M.J. 23 December1996b. Grasses of the Canadian Arctic Archipelago: descrip-tions, illustrations, identification, and information retrieval.<http://www.keil.ukans.edu/delta> (accessed October 2000).

Arnold, M.L., Buckner, C.M., and Robinson, J.J. 1991. Pollen-mediated introgression and hybrid speciation in Louisiana irises.Proc. Natl. Acad. U.S.A.88: 1398–1402.

Bashaw, E.C., and Hanna, W.W. 1990. Apomictic reproduction.InReproductive versatility in the grasses.Edited byG.P. Chapman.Cambridge University Press, Cambridge, U.K. pp. 100–130.

Bay, C. 1993. Taxa of vascular plants new to the flora of Green-land. Nord. J. Bot.13: 247–252.

Böcher, T.W., Holmen, K., and Jacobsen, K. 1968. The flora ofGreenland. English edition. P. Haase & Son, Copenhagen, Den-mark.

Boivin, B. 1967. Énumération des plantes du Canada. VIMonopsides (2ème partie). Nat. Can.94: 471–528.

Boivin, B., and Löve, D. 1960.Poa agassizensis, a new prairiebluegrass. Nat. Can.87: 173–180.

Cayouette, J. 1984. Additions and extensions d’aire dans la florevasculaire du Nouveau-Québec. Nat. Can.111: 263–274.

Cayouette J., and Darbyshire, S.J. 1993. The intergeneric hybridgrass “Poa labradorica.” Nord. J. Bot.13: 615–629.

Choo, M.K., Soreng, R.J., and Davis, J.I. 1994. Phylogenetic rela-tionships amongPuccinelliaand allied genera of Poaceae as in-ferred from chloroplast DNA restriction site variation. Am. J.Bot. 8: 119–126.

Clayton, W.D., and Renvoize, S.A. 1986. Genera Graminum:grasses of the world. Kew Bull. Add. Ser. XIII.

Cody, W.J. 1996. Flora of the Yukon Territory. NRC ResearchPress, Ottawa, Ont.

Consaul, L.L., and Gillespie, L.J. 2001. A re-evalution of specieslimits in Canadian Arctic IslandPuccinellia (Poaceae): resolv-ing key characters. Can. J. Bot.79. In press.

Demesure, B., Sodzi, N., and Petit, R.J. 1995. A set of universalprimers for amplification of polymorphic non-coding regions ofmitochondrial and chloroplast DNA in plants. Mol. Ecol.4:129–131.

de Wet, J.M.J. 1986. Hybridization and polyploidy in the Poaceae.In Grass systematics and evolution.Edited byT.R. Soderstrom,

© 2001 NRC Canada




K.W. Hilu, C.S. Campbell, and M.E. Barkworth. SmithsonianInstitution Press, Washington, D.C. pp. 188–194.

de Wet, J.M.J., Newell, C.A., and Brink, D.E. 1984. Counterfeithybrids betweenTripsacumand Zea. Am. J. Bot.71: 245–251.

Dowling, T.E., Moritz, C., Palmer, J.D., and Rieseberg, L.H. 1990.Nucleic acids III: analysis of fragments and restriction sites.InMolecular systematics. 2nd ed.Edited by D.M. Hillis, C.Moritz, and B.K. Mable. Sinauer Associates, Sunderland, Mass.pp. 249–320.

Doyle, J.J., and Doyle J.L. 1990. Isolation of plant DNA fromfresh tissue. Focus,12: 13–15.

Dumoulin-Lapègue, S., Pemonge, M.-H., and Petit, R.J. 1997. Anenlarged set of consensus primers for the study of organelleDNA in plants. Mol. Ecol.6: 393–397.

Edmondson, J.R. 1978. Infrageneric taxa in EuropeanPoa L. Bot.J. Linn. Soc.76: 329–334.

Edmondson, J.R. 1980.PoaL. In Flora Europaea. Vol. 5.Edited byT.G. Tutin, V.H. Heywood, N.A. Burges, D.M. Moore, D.H.Valentine, S.M. Walters, and D.A. Webb. Cambridge UniversityPress, Cambridge, U.K. pp. 159–167.

Felsenstein, J. 1985. Confidence limits on phylogenies: an ap-proach using the bootstrap. Evolution,39: 783–791.

Fredskild, B. 1996. A phytogeographical study of the vascularplants of West Greenland. Medd. Grønl.45: 1–157.

Gillespie, L.J., Consaul, L.L., and Aiken, S.G. 1997. Hybridizationand the origin of the arctic grassPoa hartzii(Poaceae): evidencefrom morphology and chloroplast DNA restriction site data.Can. J. Bot.75: 1978–1997.

Harris, S.A., and Ingram, R. 1991. Chloroplast DNA andbiosystematics: the effects of intraspecific diversity and plastidtransmission. Taxon,40: 393–412.

Kellogg, E.A. 1987. Apomixis in thePoa secundacomplex. Am. J.Bot. 74: 1431–1437.

McLachlan, K.I., Aiken, S.G., Lefkovitch, L.P., and Edlund, S.A.1989. Grasses of the Queen Elizabeth Islands. Can. J. Bot.67:2088–2105.

Müntzing, A. 1933. Apomictic and sexual seed formation inPoa.Hereditas,27: 131–154.

Murray, D.F. 1995. Causes of arctic plant diversity: origin and evo-lution. In Arctic and Alpine Biodiversity.Edited byF.S. Chapinand C. Korner. Springer-Verlag, Berlin. pp. 33–43.

Nannfeldt, J.A. 1935. Taxonomical and plant-geographical studiesin the Poa laxagroup. Symb. Bot. Ups.1(5): 1–113.

Nannfeldt, J.A. 1940. On the polymorphy ofPoa arcticaR.Br. withspecial reference to its Scandanavian forms. Symb. Bot. Upsal.4(4): 1–85.

Olonova, M.V. 1993. Phenogeographical study ofPoa glaucaVahl.Sib. Biol. Zh. 6: 70–74.

Palmer, J.D., Jansen, R.K., Michaels, H.J., Chase, M.W., andManhart, J.R. 1988. Chloroplast DNA variation and plant phy-logeny. Ann. Mo. Bot. Gard.75: 1180–1206.

Polunin, N. 1940. Botany of the Canadian Eastern Arctic. Part 1.Bull. Natl. Mus. Can. No. 92.

Polunin, N. 1959. Circumpolar arctic flora. Clarendon Press, Ox-ford, U.K.

Porsild, A.E. 1943. Materials for a flora of the continental North-west Territories of Canada. Sargentia,4: 1–79.

Porsild, A.E. 1955. The vascular plants of the western CanadianArchipelago. Bull. Natl. Mus. Can. No. 135.

Porsild, A.E. 1957. Illustrated flora of the Canadian Arctic Archi-pelago. Bull. Natl. Mus. Can. No. 146.

Porsild, A.E. 1964. Illustrated flora of the Canadian Arctic Archi-pelago. 2nd ed. revised. Bull. Natl. Mus. Can. No. 146.

Porsild, A.E., and Cody, W.J. 1980. Vascular plants of continentalNorthwest Territories, Canada. National Museum of Natural Sci-ences, National Museums of Canada, Ottawa, Ont.

Probatova, N.S. 1984. New taxa of the Poaceae from the far east ofthe USSR [in Russian.] Bot. Zh. (Kiev),69: 251–259

Reiseberg, L.K., and Soltis, D.E. 1991. Phylogenetic consequencesof cytoplasmic gene flow in plants. Evol. Trends Plants,5: 65–84.

Rønning, O.I. 1996. Flora of Svalbard. 3rd ed. Norsk Polarinstitutt,Oslo. Polarhåndb. No. 10.

Saghai-Maroof, M.A., Soliman, K.M., Jorgensen, R.A., and Allard,R.W. 1984. Ribosomal DNA space-length polymorphism in bar-ley: Mendelian inheritance, chromosomal location, and popula-tion dynamics. Proc. Natl. Acad. U.S.A.81: 8014–8018.

Sambrook, J., Fritsch, E.F., and Maniatis, T. 1989. Molecular clon-ing: a laboratory manual. 2nd ed. Cold Spring Harbour Labora-tory Press, Cold Spring Harbor, N.Y.

Scholander, P.D. 1934. Vascular plants from northern Svalbard.Skr. Svalbard Ishavet.62: 1–153.

Scoggan, H.J. 1978. Gramineae (Grass family).In The flora ofCanada. Natl. Mus. Nat. Sci. (Ottawa) Publ. Bot. No. 7.pp. 218–337.

Simmons, H.G. 1906. The vascular plants in the flora ofEllesmereland. Report of the Second Norwegian Arctic Expedi-tion in the “Fram” 1898–1902. No. 2. The Society of Arts andSciences of Kristiania. Kristiania, Norway.

Soltis, D.E., Soltis, P.S., and Mulligan, B.G. 1992. Infraspecificchloroplast DNA variation: systematic and phylogenetic consider-ations.In Molecular systematics of plants.Edited byP.S. Soltis, D.E.Soltis, and J.J. Doyle. Chapman & Hall, New York. pp. 117–150.

Soreng, R.J. 1990. Chloroplast-DNA phylogenetics and biogeographyin a reticulating group: study inPoa (Poaceae). Am. J. Bot.73:1383–1400.

Soreng, R.J. 1991a. Systematics of the “Epiles” group ofPoa(Poaceae). Syst. Bot.16: 507–528.

Soreng, R.J. 1991b. Notes on new infraspecific taxa and hybrids inNorth AmericanPoa (Poaceae). Phytologia,71: 390–413.

Soreng, R.J. 1998. An infrageneric classification forPoa in NorthAmerica, and other notes on sections, species, and subspecies ofPoa, Puccinellia, andDissanthelium(Poaceae). Novon,8: 187–202.

Soreng, R.J., and Barrie, F. 1999. Proposal to conserve the namePoapratensis(Poaceae) with a conserved type. Taxon,48: 157–159.

Soreng, R.J., and Davis, J.I. 2000. Phylogenetic structure in Poaceaesubfamily Pooidae as inferred from molecular and morphologicalcharacters: misclassification versus reticulation.In Proceedings, 3rdInternational Symposium on Grass. Systematics and Evolution,1998.Edited byS.W.L. Jacobs and J. Everett. Commonwealth Sci-entific and Industrial Research Organization, Collingwood, Austra-lia. pp. 61–74.

Soreng, R.J., and Kellogg, E.A. 2001.Poa. In Flora of North America.Edited byFlora of North America Editorial Committee. Oxford Uni-versity Press, New York. In press.

Soreng, R.J., Davis, J.I., and Doyle, J.J. 1990. A phylogenetic anal-ysis of chloroplast DNA restriction site variation in Poaceaesubfam. Pooideae. Plant Syst. Evol.172: 83–97.

Swofford, D.L. 1998. PAUP* phylogenetic analysis using parsi-mony (*and other methods), version 4 edition. Sinauer Associ-ates, Sunderland, Mass.

Taberlet, P., Gielly, L., Pautou, G., and Bouvet, J. 1991. Universal prim-ers for amplification of three non-coding regions of chloroplastDNA. Plant Mol. Biol. 17: 1105–1109.

Tremblay, N.O., and Schoen, D.J. 1999. Molecular phylogeographyof Dryas integrifolia: glacial refugia and postglacial re-colonization. Mol. Ecol.8: 1187–1198.

© 2001 NRC Canada

700 Can. J. Bot. Vol. 79, 2001



© 2001 NRC Canada


Tzvelev, N.N. 1976. Grasses of the Soviet Union [in Russian.]Zlaki SSSR, Nauka, Leningrad, Russia.[Translation from Rus-sian by Amerind Publishing Co., New Dehli, 1983].

Tsvelev, N.N. 1964.PoaL.—bluegrass.In Flora of the Russian Arc-tic. Arkticheskaya flora SSSR, Vol. 2 (Gramineae).Edited byA.I.

Tolmachev. USSR Academy of Sciences, Komarov BotanicalInsititute [Translated from Russian by G.C.D. Griffiths.Edited byJ.G. Packer. University of Alberta Press, Edmonton, 1995].



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