From Fossils to Molecules:The Metasequoia Tale Continues

Hong Yang

Recent studies of the wild population in China using the techniques of cuticle

micromorphology and population genetics have introduced new ideas aboutthe evolutionary history of Metasequoia glyptostroboides, previously limited to

hypotheses drawn from the fossil record. The new information suggests that

the living Metasequoia trees may be recent immigrants to their remote valley incentral China, rather than Tertiary relics dating back as far as 15 million years ago.

y first encounter with the genus< , Metasequoia occurred more than fif-V1 teen years ago when I was a college

student in Wuhan, a city along the YangtzeRiver in the Hubei Province of central China. Ina paleobotany lab session, I was shown a fossilof Metasequoia foliage collected from a Tertiarydeposit in northeastern China; minutes laterI was led outside to inspect the city tree

of Wuhan-living dawn redwoods plantedalong roadsides. Seeing the close resemblancebetween a fossil imprint preserved in a rockfor over 50 million years and the green leaves

shining in front of my eyes was a breathtakingexperience. Equally astounding to me was thestory of Metasequoia glyptostroboides, thedramatic discovery of a living tree previouslyknown to science only as a fossil, a story thathad unfolded in that same province in the early1940s (Hu 1948, Merrill 1948). What I couldnot foresee was that this college exercise hadplanted a seed in my mind that later grew into astrong professional attachment to this species.The dawn redwood legend has led me twice to"Metasequoia Valley" in central China andengendered a tremendous interest in pursuingits evolutionary history through both fossilrecords and DNA molecules.

I came to the United States in 1988 for gradu-ate training under Professor Charles J. Smiley atthe Tertiary Research Center of the Universityof Idaho, and it was there, in Smiley’s personallibrary, that I read intensively in the literatureon both modern and fossil Metasequoia.lSmiley had been a graduate student of ProfessorRalph W. Chaney, the first Western scientist totravel to Metasequoia Valley, in 1948, and inSmiley’s files were copies of remarkable photo-graphs that Chaney and his traveling compan-ion had taken during their trip there shortlyafter the discovery of the living trees.

In 1988, Smiley was conducting research onthe Clarkia Miocene fossil site, an exceptionallywell-preserved fossil deposit in northern Idahothat contained abundant Metasequoia fossils aswell as other warm-temperate plant genera thatChaney had observed during his trip to Metase-quoia Valley. I was interested in the theory of"Arcto-Tertiary flora" that Chaney had put for-ward to explain the origin and distribution ofplants around the Pacific basin. He argued thatMetasequoia and the plants associated with itoriginated in the high northern latitudes duringthe Cretaceous period, over 65 million yearsago; then the whole assemblage was graduallypushed southward into the modern Metase-

1 After Dr. Smiley’s sudden passmg on January 1, 1996, his personal library was donated to the Nanjing Instituteof Geology and Paleontology, the Chinese Academy of Sciences.

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The oldest Metasequoia tree m Xiaohe Commune, estimated at 440years of age, photographed m 1997. Photographs taken m 1948 and 1980can be seen on pages 36 and 49, respectmely.

to complete the journey fromWanxian (known as Wan Hsienin the old spelling) to Moudao(also known as Mo-tao-chi) thatChaney completed in three

days in 1948. Still, the narrowroad and steep slopes remindedme of a poem by Li Bai, thegreat poet of the Tang Dynasty,who described traveling in themountains of Sichuan as beingas difficult as climbing to thesky. Although the hardwoodforest that Chaney had seengrowing alongside the dawnredwoods had been cut downover the previous forty years,the enormous, centuries-olddawn redwood that Chaney hadadmired in Moudao still stoodproudly in the middle of farm-land, and I could not help butbe amazed by its power to

endure time and environmental

change. Touching the tree’sreddish bark and looking up atits top branches, I had to won-der when and how it got there,and why the species survivesonly in this remote valley. Theanswers to my questions, it

seemed, were to be found onlyin the fossil record.

For Chaney, the discovery ofliving Metasequoia provided acritical piece of evidence insupport of his theory, but sincehis time, more fossil Metase-quoia have been reported. I

quoia Valley during the Tertiary, beginningaround 40 million years ago when the global cli-mate started to cool. A trip to Metasequoia Val-ley to trace Chaney’s steps among the "livingTertiary flora" appealed to both Smiley and me.

Historical Biogeography Revealed by ItsFossil Record

In June 1990 Professor Smiley, his wife Peg, Pro-fessor Fred Johnson, a forest ecologist from theUniversity of Idaho, and I took only four hours

wanted to find out if Chaney’s theory was stillvalid in light of new findings from China, Japan,and Russia. Shortly after our trip to Metase-quoia Valley, I started to compile the Metase-quoia fossil record from the Cretaceous onward,and a more detailed picture of Metasequoia his-tory started to emerge (Yang and Smiley 1991). ~.It is apparent that the story of this remarkabletree encompasses the entire history of theNorthern Hemisphere over the past 100 millionyears, including the changes in land connec-

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tions and climates and the evolution of livingorganisms.The up-to-date fossil record reveals the fol-

lowing four major phytogeographic events inthe history of this genus:

First, it is likely that Metasequoia firstevolved in eastern Russia (about 60 degreesNorth) during the early Late Cretaceous period,around 100 million years before the present, asthe earliest dawn redwood fossils were reportedfrom this region. Thanks in part to the low tem-perature gradient across the Northern Hemi-sphere and the Bering land connection betweenNorth America and eastern Eurasia, Metase-quoia spread very rapidly in two opposite direc-tions shortly after its origin: southward to lowerlatitudes in eastern Russia, northern Japan, andnortheastern China; and northward across theBering land connection to North America. Bythe end of the Cretaceous, when dinosaursbecame extinct, Metasequoia had traveled as farsouth as New Mexico (about 35 degrees North)in North America and had become a dominanttree in ancient forests of southern Japan (about36 degrees North) in Asia.

Second, during the Paleocene, about 60 mil-lion years ago, Metasequoia moved to the highlatitudes of North America and invaded north-ern Europe to become a prominent member inancient floras circumscribing the North Pole. Atthe same time, Metasequoia maintained thedistribution pattern at lower latitudes aroundthe Pacific basin that it had established duringthe Late Cretaceous.

Third, when major global cooling occurredduring the Late Eocene, 40 million years ago,and the cooler climate persisted, the distribu-tion pattern changed dramatically: Metasequoiadisappeared from high latitudes. By the EarlyOligocene, 35 million years before present,Metasequoia had moved to lower latitudes andundertaken a longitudinal expansion to arrivein central Eurasia along the foothills of theUral Mountains. During the Middle Miocene,when the climate again warmed up, Metase-quoia re-entered the Arctic Circle. It had van-ished from Eurasian fossil floras by the MiddleMiocene and from North America by the end ofthe Miocene.

(continued on page 65)

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Fossil Remains of MetasequoiaThe discovery of living Metasequoia in Chinamore than fifty years ago shed light on the studyof fossil Taxodiaceae, the family of redwoodsand bald cypresses. After his trip to China,Chaney (1951) reassigned to the genus Metase-quoia many fossils that had been misidentifiedas Taxodium or Sequoia. Since then, newMetasequoia fossils have been reported fromthe Northern Hemisphere, the oldest datingback to the Late Cretaceous. Metasequoia foli-age and cones are among the most common fos-sils in Paleocene and Eocene floras around thePacific Ocean. From small branchlets to singleshoots, the leaves of Metasequoia show mor-phological characteristics that differ from thoseof other members of Taxodiaceae.The graceful, opposite arrangement of leaves

allows quick, sure identification in the field(figure aJ. However, reliable identification is dif-ficult in pollen and wood fossils of Metase-quoia : separated from the male cone,

Metasequoia fossil pollen grains are almostindistinguishable from those of members ofCupressaceae, Taxaceae, or other Taxodiaceae;likewise, its wood anatomy is very similar tothat of other members of the same family.Metasequoia fossils have been reported from

exceptionally well preserved deposits, revealingmorphological and anatomical details of dawnredwoods that lived millions of years ago. Forexample, three-dimensional Metasequoia fossilcones from the Clarkia Miocene lake depositin Idaho yielded seeds that give an accurate

description of Metasequoia seeds in Miocenetime (figure bJ. Mummified Metasequoia leavesfound in an Eocene deposit on Axel HeibergIsland in Canada’s Arctic archipelago have per-mitted detailed anatomical studies of its soft tis-sue, and leaves trapped in amber for more than50 million years at Fushun, a Paleocene-to-Eocene coalfield in northern China, offer aremarkably detailed snapshot of an ancientMetasequoia.

Metasequoia leaves trapped m amber found in aPaleocene coal mme m Fushun, Chma

Metasequoia fossil remains: shoots (a) and female cone with seeds (b) from the ClarkiaMiocene deposit m northern Idaho.

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Metasequoia fossil distnbution through geo-logical times. NP: North Pole, C: Center ofOrigm, TC: Tropic of Cancer, EQ: Equator.

(a) Late Cretaceous (100 milhon yearsbefore present, or MYPB); (b) Paleocene (65 to54 MYBP); (c) Eocene (54 to 38 MYBP); (d)Oligocene (38 to 24 MYBP); (e) Miocene (24 to5 MYBP); (f) Phocene (5 to 2 MYBP); (g) EarlyPleistocene (2 MYBP to present). The squaremarks the modern Metasequoia Valley.

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The fossil record shown on the precedingpage was compiled from published paleobo-tanical literature, using only clearly illus-trated fossil leaves and cones. These recordsgive a feeling for the extensive distributionof Metasequoia. The oldest was found inLate Cretaceous rocks (about 100 millionyears old) in northeastern Russia. At theother extreme, the youngest Metasequoiafossil was collected from Pleistocene depos-its in southwestern Japan: the lower part ofthe Osaka Group-about 1.6 million yearsold-marks the extinction of Metasequoiafrom Japan.The highest latitude at which a Metase-

quoia fossil has been reported is 82 degreesNorth in northeastern Greenland, whereabundant Paleocene fossils have beenfound. The prize for southernmost distri-bution goes to the Shihti Formation, aMiocene deposit in Taiwan at a latitude of25 degrees North. To the west, Metasequoiafossils have been reported from Oligocene _

deposits in central Asia as far as 60 degreesEast.

Possible Metasequoia dispersal and migrationroutes: (a) center of omgm; (b) Paleocene

dispersal paths showmg invasion of higherlatitudes ; (c) lateral Ohgocene dispersal paths,(d) Late Pliocene or Early Pleistocene migrationdirection.

(continued from page 62)

Fourth, the post-Miocene history ofMetasequoia has been less studied, yet it iscritical to the explanation for its survival incentral China. Metasequoia fossils from thePliocene and Pleistocene epochs-roughlyfrom 5 to 1.7 million years ago-have beenfound only in central and southern Japan.Non-marine Pliocene and Pleistocene depos-its have been commonly reported in easternChina, but no Metasequoia fossil has beenfound. If we read the fossil record literally, itsuggests that the living Metasequoia is geo-logically a newcomer to its valley at the junc-ture of Sichuan, Hubei, and Hunan Provincesin central China, most likely having immi-

_ grated from Japan during the Late Pliocene or

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These isolated trees are located m a field mside an iron fence m theremote Longshan area of Hunan Province, about 70 miles southeast ofMetasequoia Valley.

Early Pleistocene, only 2 million years or lessbefore the present.

It is interesting to note that the morphologyof Metasequoia has changed little during the100 million years since its origin. A recent taxo-nomic revision of Metasequoia fossils by Liuet al. (1999) has reassigned twenty of what wereformerly twenty-one species (excluding only M.millen) to a single species: M. occidentalis. Thismerger suggests a considerable degree of mor-phological stasis and implies a slow rate ofmorphological evolution. This would explainthe striking similarity in morphology between

the Tertiary fossil and themodern Metasequoia twig thatI compared fifteen years agoin Wuhan.

Morphological Variation atthe Population LevelIn 1997, seven years after myfirst trip, I revisited Metase-

quoia Valley with colleaguesfrom the Nanjing Institute ofGeology and Paleontology, theChinese Academy of Sciences.The aim of the second trip wasto collect modern Metasequoialeaf samples from trees in thewild for study of both cuticleand genetic variations at thepopulation level. In the pastfew years, China’s market

economy has reshaped the

country, and I was eager to seehow these trees had weatheredthe environmental changesthat accompanied economicreform. To my surprise, therapid economic growth thathas taken place elsewhere inChina had not penetrated theremote Metasequoia Valley.And thanks to the Metasequoiaconservation program, most ofthe wild trees are still healthy,although I was sad to learn thateight huge trees under whichwe picnicked in 1990 had died acouple of years ago.

On this trip, we made a special effort to travelto the remote Longshan area of Hunan Province,about 110 kilometers (70 miles) southeast ofMetasequoia Valley, to visit and sample leavesfrom several large, wild trees that have rarelybeen seen by outsiders. We also sampled leavesfrom large Metasequoia trees in eight naturaldawn redwood groves in the provinces ofSichuan and Hubei. Each sample was dividedinto two sets: one for study of cuticle micromor-phology and another for DNA analysis. Cuticlefrom each tree was prepared and examinedunder a scanning electron microscope by Qin

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Leng, a paleobotanist at the Nanjing Institute ofGeology and Paleontology. We were not sur-prised to find that the cuticular characteristicsamong living trees within Metasequoia Valleydisplay little variation, but Leng did make anexciting discovery: the sample collected from anisolated wild tree in Paomu, Longshan, showedsome variation. Among other noticeable differ-ences, the internal surface of the lower cuticlein the Longshan leaves possesses a uniquelyeven cuticular membrane between the stomatalzone and the non-stomatal zone-a characteris-tic that is not observed in any of the groves.2

Moreover, compared with all other samples,the Paomu sample also showed variation in themicromorphology of its guard cells. The differ-ences in these features are great enough to war-rant designation of two separate cuticle types,and the data imply that the isolated tree inHunan Province may have preserved some char-acteristics that do not exist in the trees in

Metasequoia Valley. Is this an indication thatthis isolated dawn redwood possesses a slightlydifferent gene pool? If so, it is exciting news forthe endangered Metasequoia population, whosegenetic variability is expected to be very low.New morphological features found in the wildpopulation may signal an increase of geneticdiversity, which would help to alleviate itsendangered state.

Clues from DNA Molecules

The past fifty years have witnessed the rapiddevelopment of molecular biology, and theimpact of DNA-based biotechnology is felt inalmost all subdisciplines of biological science.Earlier genetic work on Metasequoia has exam-ined chromosome characteristics and, morerecently, electrophoretic patterns of enzymepolymorphism (Kuser et al. 1997), but popula-tion structure at the DNA level for wild Metase-

quola remained unexplored. Accordingly, a setof leaf samples collected during our 1997 tripwas used to assess genetic diversity; the projectis still in progress, but some preliminary dataare intriguing.As a small population with a very limited

number of individuals living in a restricted geo-

In 1992, the postoffice of the People’s ’s

Repubhc of Chinaissued stampscelebrating dawnredwood as well asother prommentChmese comfers.

graphic area, we would expect the modernMetasequoia population to display a very lowlevel of genetic diversity, especially since themorphology of several of its features has shownconsiderable homogeneity at the populationlevel. However, preliminary DNA analysis,using a RAPD (random amplified polymorphicDNA) technique, by Dr. Qun Yang and his stu-dent Chunxiang Li at the Nanjing Institute ofGeology and Paleontology indicates that thespecies possesses a moderate genetic diversitythat exceeds that of other endangered Chineseconifers, such as Cathaya argyrophylla. Further,the RAPD analysis also reveals that the geneticdifferences among sampled Metasequoia treesis primarily related to the geographic distancebetween them (Li et al. 1999). This interestingrevelation suggests several possibilities: First,the genetic constitution of isolated trees inHunan Province may have helped to increasethe overall genetic diversity of the population.If this is true, the data from molecular analysiscould fit with the findings in the comparison ofcuticle morphology, which also imply a slightlydifferent gene pool for the grove in HunanProvince from that of the groves in MetasequoiaValley.

Second, the unexpected level of genetic diver-sity may reflect a relatively recent establish-

(contmued on page 69)

2 Q. Leng, H. Yang, Q. Yang, and J-p. Zhou 1999. Variation of cuticle micromorphology m native population ofMetasequoia glyptostroboides Hu et Cheng ~Taxodiaceae~ (m progress).

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A Glimpse of the Living PopulationCuticle is a waxy layer covering the outer cellwalls of the plant leaf that serves as an effectivebarrier against water loss. Both botanists andpaleobotanists are interested in plant cuticlebecause their faithful impressions of epidermalcells provide valuable physiological and some-times taxonomic information. The cuticle’sstable chemistry allows it to be preserved insedimentary rocks for millions of years; there-fore, it is particularly valuable for paleo-botanists, who use it to classify fossil plantsand infer their paleoenvironment. However, forboth botanist and paleobotanist, studies of fos-sil cuticle are greatly improved when precededby analysis of the cuticle micromorphology ofliving plants, and the limited distribution ofexisting Metasequoia will simplify this task ofexamining the variability of cuticle micromor-phology within the species. Thus, the results ofthese studies will be very useful for interpretingcuticular features in the fossil material.

In the laboratory, cuticle from both sides ofMetasequoia leaves can be prepared, and bothinternal and external surfaces of each piece canbe examined. Cuticle is separated from the leafby means of an acid solution. After the materialis washed in distilled water and dried in the air,it can be coated with platinum and then ampli-fied hundreds of times under a scanning elec-tron microscope. In addition to the cuticle’sthickness, micromorphological features of taxo-nomic or physiological value include the shapeof epidermal cells, size and shape of stomata,shape of guard cells around stomata, and pat-terns on various cell walls.Two types of cuticle micromorphology were

observed by Qin Leng in the wild Metasequoiapopulation. The isolated tree growing in theLongshan area of Hunan Province exhibitsslightly different cuticle characteristics fromthose of trees in the Sichuan and Hubei groves,some 110 kilometers (70 miles) away. Forexample, epidermal walls in the Paomu samplefrom Longshan are more regular, with a definedboundary, and the shape of the guard cellsaround stomata differs from those of theSichuan and Hubei samples. These differencespoint to a possible source of morphologicalvariation in the wild population.

Cuticle micromorphology of Immg Metasequoiamagmfied 200 times, both show the mternal surfaceof the cuticle on the underside of the leaf, comparingthe two cuticle types: (a) from an isolated tree mLongshan, Hunan Provmce, (b) from MetasequoiaValley m Lichuan, Hubei Provmce.

DNA from MetasequoiaOnly recently have molecular approaches beenapplied to the field of paleobiology, providingevolutionary biologists with an independentdata set that helps compensate for the incom-plete fossil record. In higher plants, DNA mol-ecules reside in the nucleus and in two

organelles, chloroplast and mitochondria. Abiochemical procedure permits a mixture ofthe three types of DNA to be extracted and

purified from plant cells. Then, using a newmolecular technique called polymerase chainreaction (PCR)-a kind of molecular copymachine-selected portions of the DNA canbe amplified into millions of identical copies.Depending on the goals of the research, ampli-fied DNA fragments can be sequenced to revealnucleotide base pairs or can be cut by variousenzymes to detect variations. It is the variationin DNA molecules that is the genetic basis

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Agrose gel electrophoresis pattern showmg RAPDamphficatlons demved from 27 different mldMetasequoia trees.

for morphological variability and populationdiversity.RAPD (random amplified polymorphic DNA)

analysis, a PCR-based technique, is a newmolecular tool that has proved powerful indetecting genetic diversity at the populationlevel. Primers-small synthetic pieces ofDNA-will locate any regions of the chromo-some ("priming sites") that exhibit sequencescomplementary to the primers’ sequences. PCRwill amplify all complementary fragments ofDNA; if, due to a mutation, a priming site isabsent from an individual, then PCR will skipover it. Thus, by counting the number of frag-ments shared by two individuals we get a crudemeasure of their genetic difference.When fragments from each Metasequoia

sample are separated and stained according totheir size, a series of bands is created. Variationsin amplification patterning among the samplesmirror the underlying DNA variation of theMetasequoia population. Therefore, the amountof genetic variation within the population canbe measured by the pattern of bandmg afteramplification. By comparing amplified bands,computer-based statistical programs are ableto calculate the genetic divergence amongexammed Metasequoia samples. For DNAcollected from any two individual trees, themore differences among the bands, the largerthe genetic distance.

Only in the past few years has ancient DNAfrom amber been extracted and sequenced. Ihave cracked open an amber from Fushan con-

taining a Metasequoia shoot similar to thatshown on page 63, hoping to find ancient genesthat had survived for over 50 million years.Despite repeated efforts, I have been unable tofind DNA; perhaps this goal will be achieved inthe future.

(continued from page 67Jment of the living population. In theory, thelonger a population exists in a confined area,the more homogeneous its genetic diversitywould become as inbreeding increases.

Third, the unexpected level of geneticdiversity may also indicate divergent evolu-tion of small, isolated populations due tohabitat fragmentation from a once geneticallyhomogeneous, large population. Unfortu-nately, our current data are insufficient toprove or disprove these possibilities. TheRAPD technique used in this study is a rough,molecular-level survey and, moreover, thesample size is not large enough for a meaning-ful statistical test. DNA sequences of appro-priate genes derived from individualMetasequoia may yield more quantitativeinformation. Nonetheless, the available DNAdata reveal an interesting level of geneticvariation in the wild Metasequoia population.

When Did Metasequoia Arrive There?

Traveling through Metasequoia Valley in1948, Chaney thought that he had seen a Ter-tiary fossil flora come to life. Based on theclose resemblance between fossil remainsthat he had studied in Tertiary depositsaround the Pacific basin and living plants thathe encountered in Metasequoia Valley,Chaney believed that Metasequoia and itsTertiary associates had taken refuge in centralChina since Tertiary time. He asserted thatMetasequoia "participated in wide migra-tions" from north to south and "continueddown to the present Metasequoia valley"(Chaney 1948). In other words, he viewed theliving Metasequoia as a Tertiary relic. How-ever, the detailed fossil record seems to tell a

slightly different story.The absence of post-Miocene Metasequoia

fossils in China suggests that the dawn red-wood is a relatively recent arrival in centralChina. The youngest Metasequoia fossilsfound in China are from Middle Miocene

deposits (about 15 million years before

present) in Jilin Province, more than 2,000kilometers (1,240 miles) northeast of Metase-quoia Valley, and in Taiwan, an island morethan a thousand kilometers (620 miles) east of

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the present native population. Despite fiftyyears of intensive searching (Li 1995), no post-Miocene Metasequoia has ever been foundin China. It is possible, of course, that youngerMetasequoia fossils are waiting to be discoveredin central China, but it is also conceivablethat the chronological and geographical gapin the fossil record reflects the tree’s absence

during the period of more than 15 millionyears between the Middle Miocene and EarlyPleistocene.

Pliocene and Pleistocene Metasequola fossilshave been found only in central and southernJapan. Geological evidence shows that the landlink between southern Japan and eastern China(at about 34 to 36 degrees North) was availablemost recently during the late Pliocene to earlyPleistocene interval, during the same periodthat Metasequoia trees are known to have livedin southern Japan. This land connection couldhave provided a migration route for its west-ward relocation (Wang 1985).There is also evidence that, while the climate

in Japan during the Pliocene appears to havebeen suitable for Metasequoia, the aridity ofcentral China in that period would not haveallowed it to survive. Conversely, during thePleistocene "Ice Age," southern Japan may havebecome too cold for Metasequoia (Momohara

1992), while central China, which was not sig-nificantly influenced by continental glaciation,thanks to the intervening mountains, couldhave been a protected haven for the species. Onepossible interpretation of the fossil distributionand climate data is that Metasequoia migratedsouthward during the Late Pliocene or EarlyPleistocene from Japan to the modern Metase-quoia Valley.

Finally, the preliminary RAPD data seem tobe compatible with the fossil record, suggestingthe recent establishment of Metasequoia in itspresent range. Unfortunately, it offers no preciseinformation regarding the antiquity of the livingpopulation, but further molecular study mayyield better data.

Conservation Efforts

During my second visit to Metasequoia Valley,I was happy to see promising results from localconservation efforts, including preservation oflarge trees in the wild, a plantation of graftedtrees, and reintroduction of seedlings to otherparts of China and throughout the world.Despite a very limited budget, a Metasequoiaconservation station in Xiaohe, with Mr.Shenhou Fan as the director and only employee,has maintained a large Metasequoia seedlingfarm and a plantation grown from grafts of wild

Long He, Hubei, 1994. In Chma, Metasequoia has been planted m groves and along roads m great numbers,and many nurseries have been estabhshed to produce seedlmgs for cuttings. The rooting efficiency of cuttmgsdecreases with the age of the source tree; the best source of cuttmgs is from seedlmgs aged one to three years

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trees. Local people still worship the gianttrees, believing they bring the family goodluck (nowdays translated into prosperity) andbless their children with healthy bodies andbright minds. Educational programs are increas-ing, as is local awareness of the significance ofthese trees. Many articles in the Chinese presshave featured Metasequoia, describing its dis-covery, scientific value, and current conserva-tion programs.Over the next fifteen years or so, the Metase-

quoia trees will witness the construction of thecontroversial Three Gorges Dam on the YangtzeRiver, not far from their native land. The hugemanmade lake behind the dam is bound toaffect the local climate and related ecosystems.It is my hope that the remarkable resilience ofthis species will again enable it to cope withdramatic environmental changes, as it has sosuccessfully done throughout its history.

Fifty years may be short for the dawn redwoods,whose lifespans easily exceed hundreds of years,but it is long enough for political, economic, andtechnological changes to occur around theirnative valley. Our knowledge of these magnifi-cent trees has grown substantially over the pastfifty years, thanks to new technologies and toseveral generations of industrious scientists. Asstudies of the species continue to provide scien-tists with new inputs for new ideas and hypoth-eses, the fascinating Metasequoia tale willcontinue to evolve.

Literature Cited

Chaney, R. W. 1948. The bearing of the livingMetasequoia on problems of Tertiarypaleobotany. Proceedings of the NationalAcademy of Sciences, USA 34/11): 503-515.

1951. A revision of fossil Sequoia and Taxodmmm western North America based on the recent

discovery of Metasequoia Transactions of theAmerican Philosophical Society, New Senes,

’

40(3): 171-262Hu, H. H 1948 How Metasequoia, the "hvmg fossil," "

was discovered m Chma. Journal of the NewYork Botanical Garden 49: 201-207.

Kuser, J. E., D. L. Sheely, and D. R Hendricks. 1997.Genetic variation in two ex situ collectionsof the rare Metasequoia glyptostroboides(Cupressaceae). Silvae Genetica 46(5) : 258-264.

Li, X-x (ed.). 1995. Fossil floras of Chma through theGeological Ages. Guangzhou: GuangdongScience and Technology Press, 695.

Li, C-x., Q. Yang, J-p. Zhou, S-h Fan, and H. Yang.1999 RAPD analysis of genetic diversity mthe natural population of Metasequoiaglyptostroboides, central Chma. Acta Scien-tiarum Naturalmm Umversitaus Sunyatsem38/ 1 64-69.

Liu, Y-j., C-s. Li, and Y-f Wang. Studies on fossilMetasequoia from northeast Chma and themtaxonomic implications. Journal of theLinnean Society (m press).

Mernll, E. D. 1948. Another "living fossil." Arnoldia8~ 1 /:1-8.

Momohara, A. 1992. Late Pliocene plant biostratigraphyof the lowermost part of the Osaka Group,Southwest Japan, with reference to extinctionof plants. The Quaternary Research (Tokyo)31(2): 77-89.

Wang, H-z (ed.). 1985. Atlas of the Palaeogeographyof Chma. Beyng: Cartographic PubhshmgHouse, 143.

Yang, H., and C. J. Smiley. 1991. The history ofMetasequoia-Its omgm, early dispersal andmigration. Proceedmgs of the First CanadianPaleontology Conference, Program withAbstracts Vancouver, B.C., Canada, 26.

AcknowledgmentsThis article is dedicated to two scientists of previousgenerations whose work brought me to MetasequoiaDr. Ralph W Chaney, whom I never met, but whosethmkmg on Metasequoia and other fossil plants hasalways intrigued me; and Dr Charles J Smiley, withwhom I shared the ~oys of both the Clarkia fossil site mIdaho and Metasequoia Valley m Chma. I would hke tothank my colleagues at the Nanjmg Institute of Geologyand Paleontology and the Zhongshan University for theircollaboration. The research is supported by a BryantCollege course release and by summer stipends. My tripsto Chma have been supported by grants from theChmese National Science Foundation, Chma BridgeInternational, and the K. C. Wong EducationalFoundation.

Dr. Hong Yang is on the faculty of Bryant College wherehe teaches biology and earth science. He is also anadjunct research professor at the Nanyng Institute ofGeology and Paleontology, the Chmese Academy ofSciences. His research mterests lie at the mterfacebetween paleobiology and molecular biology. The authorcan be reached at the Department of Science andTechnology, Faculty Suite C, Bryant College, 1150Douglas Pike, Smithfield, Rhode Island 02917 or, viae-mail, hyang@bryant.edu.