n. 2

MONDOCACTUS

QUADERNI

An extraordinary mesem:Diplosoma retroversum Schwantesby Andrea Cattabriga

Titolo

2

MONDOCACTUS QUADERNI n. 2

An extraordinary mesem:Diplosoma retroversum Schwantesby Andrea Cattabriga.Text, drawings and pictures by the author.

Originally published onPiante Grasse,Vol XII, n° 3, Lug-Set 1992 pp. 80-85.pp. 53-56.

Digital repring November 2014.

www.mondocactus.cominfo@mondocactus.com

This work is distributed under Creative Commons License Attribution-NonCommercial-NoDerivatives 4.0 International.

Editorial

Dear reader,

the series “Mondocactus notebooks” collects a re-newed edition of the articles devoted to the succu-lent plants that I produced from 1983 until today.

The text of the articles was deliberately preserved in its original form, so any errors in grammar and concept have not been corrected. For this occasion was also produced this version of the English text, accessible by pressing the [EN] at the bottom right of each page. I apologize for the low quality of the translation, accomplished with the tools available on the internet, but its only purpose is to make the least understandable text to an international audience.

Reading the various items you can appreciate signi-ficant variations of the style adopted from time to time, due to both a gradual maturity of expression, and the need to adapt the article to the kind of pu-blication in which it was intended, it was a maga-zine of an association of amateurs, or a commercial journal.

The purpose of this project is to integrate the gene-ral information available on the mondocactus web-site pages with free downloadable documents on specific topics.

good readingAndrea Cattabriga

3 – Una straordinaria aizoacea: Diplosoma retroversum Schwantes

An extraordinary mesem:Diplosoma retroversum Schwantes

Notes on the species and comparison with other genera belonging to the sub-tribe of the mitrophyllinaeThey are many and varied the organisms that find shelter from the harshness of the hot climate of the desert burrowing into the ground; In fact, the soil of the desert or arid areas generally has a high heat insulating capacity, mainly due to its light colour. It is known that a white-coloured object, even in the sun, it keeps getting more ‘fresh’ then a dark object, as it reflects the sun’s rays. The sand of arid areas has generally muted or bright colours, such as to allow a light reflection so that almost all the energy that flows over the deserts in the form of dazzling sunlight is pushed back into space.

A plant that made the most of the opportuni-ty to obtain protection from the ground is Diplo-soma retroversum. This small mesem can be easily localized only in the winter, during the vegetative phase, when the fog and rain bring enough water and when the sun is low on the horizon. Then the plant produces its tender emerald green leaves, rich

in transparent papillae. After flowering, with the lengthening of the days, Diplosoma begins its pre-paration for the long summer break. The chlorophyll breaks down, leaving a yellowish colour to the le-aves. As the fruit continues to mature leaves are slowly drying out, holding the fruit in them. When the sun begins to be felt, in the spring, the plant does not offer outside any longer living tissue or transparent to light dots.

This little plant lives in South Africa, in the di-strict of Piquetberg, in the Cape region, an area with fairly low average temperatures. The average summer is in fact of 15 °C while the winter is 10 °C. Rainfall is in winter conditions, with rainfall between 250 and 500 mm per year. The plant lives in limestone rocks.

D. retroversum in cultivation.

4 – Una straordinaria aizoacea: Diplosoma retroversum Schwantes

The genus contains only three species, two of which are very different from each other: D. lei-poldtii and D. retroversum, while the third, Diplo-soma luckhoffii is easily distinguishable and until recently belonged to the monospecific genus Mau-ghaniella. In all cases the plants are small, acau-lescent, perennial. The roots are numerous, fine, fibrous; do not form a central taproot. The stem, like Lithops, does not develop in length, and during stasis is contained between the sole basis of the parchment residues of the dehydrated old leaves.

When in growth, Diplosoma develops opposite le-aves, united for one of the two margins, so that the body takes an asymmetric shape.

The body measuring about 25 mm or more and the free parts spread apart, with the apices fa-cing upwards; while above them are flattened and have a more or less depth central sulcus, below are rounded, mushy, glabrous, deep green and rich in transparent dots. If the plants are left to dry in the vegetation period show the first symptoms of wilting within one or two days; are therefore is not very efficient in retaining water. Watching them or touching them we can realize the extreme sensiti-vity of their skin.

The plants reach reproductive maturity one or two years after sowing, which is the only method to multiply the species. The flowers are terminal, ses-sile, solitary, reddish-pink. At the time of flowering the base of the leaves expands dramatically due to the development of the bud. This has a particular

shape of an ogive, which pushes the outside only half, then opening to let deploy the corolla.

This species in England, home of the collectors of Aizoaceae, is known for being totally unwilling to flourish. At our latitudes is punctual and flowering occurs in late winter, as well as the production of large capsules (the species is self-fertile) filled with seeds that germinate very easily.

The capsule is equipped with six or seven ni-ches, the seeds are protected by roofing membra-nes (membranes covering). The valves are opened slowly when wet, showing the bodies of relaxation that extend laterally to the valves, finishing with wings (wings valves). The poor promptness in ope-ning that these fruits show when wet (the com-plete distension of the valves in a completely wet fruit, needs 10-15 minutes) probably derives from the fact that the bodies of distension not develop medially along the full length of the valve as is the case in many other Ruschioidee.

There are bodies of closing (closing bodies). The placentation is parietal.

Comparisons with other mitrophyllinaeThe genus Diplosoma belongs to the sub-tribe of the Mitrophyllinae Schwant. together with Meye-rophytum, Mimetophyllum, Mitrophyllum and Moni-laria. These genera are characterized by a marked heterophyllia. In this article, I could not bring comments on Mimetophyllum, the genus, including those mentioned above, which is not yet in my col-lection. The heterophyllia is the characteristic that they have to bring some plants leaves with different shapes. A case is familiar to us as ivy (Hedera helix) which usually has leaves with lobed margin, and re-productive branches (those who bring flowers) the leaves are heart-shaped.

The heterophyllia in these Aizoaceae is of a type different again. At each cycle of vegetation are pro-duced two types of leaves at different times.

Leaves of type AThese are the leaves that are preserved during ae-stivation, meeting the water needs of plants during drought and are the first to return to work with the resumption of suitable conditions (they are all plants in vegetation in winter). In Mitrophyllum are greatly expanded, free from the ground and placed laterally on the stem (Fig. 1a). From the beginning to the end of the vegetation are the most important trophic organs. They collect the maximum amount of light, also thanks to their extended position. In Meyerophytum these leaves are well evident, but si-

Model of the D. retroversum fruit capsule: A - Valve,B - Membrane roofing, C - Hull or “relaxing body”, D - Valves wings.

5 – Una straordinaria aizoacea: Diplosoma retroversum Schwantes

gnificantly lower in size to those of type B (Fig. 1b). In Monilaria develop little compared to the le-aves of type B, remaining to constitute a basal body (Fig. 1e) that, already in the middle of the vegeta-tion period, begins to lose color, and dehydrating ingiallendosi, with the exception of a species, Mo-nilaria globosa, in which also these leaves are deve-loped enough (but always much less than those of type B). Perhaps this species may represent a link with Mitrophyllum or Meyerophytum. In Diplosoma these leaves do not appear at all (Fig. 1d).

Leaves of type BThey are the leaves that develop during the winter, appear between the two preceding and complete development at the end of the vegetative stage, in time to constitute, with their base, the casing to retain the new leaves of type A during aestivation. They are not free, but always in part welded to the base.

In Mitrophyllum constitute an element having the same size or slightly smaller than that of the leaves of type A, cooperating with the latter to the trophic processes until the estivazione intervenes, during which they dry completely, constituting a tunic or “miter” similar to bishop’s headdress around the new pair of leaves. In Meyerophytum have a devel-opment whose aspect ratio than those of type A is similar to what happens in Mitrophyllum. In Mo-nilaria are far more voluminous and their trophic

function is more important than that given by the leaves of type A. In Diplosoma are the only leaves to develop outside, and therefore the only ones to carry out the processes of photosynthesis.

Another character that differentiates the com-pared genera is the wood production. Mitrophyl-lum has abundant production of woody branches of a certain diameter (up to 0.8 cm or more) and rather elongated with age. Meyerophytum produc-es the long internodes as Mitrophyllum, but more attenuated; in Monilaria such production is lim-ited to short ramifications while Diplosoma hasn’t wood production, except in very limited extent in the development of very short branches, distin-guishable only by removal of the body. Within the monophyletic group of Mitrophyllinae then there is an increase in size of leaves of type A and a simultaneous reduction of the B-type in the gen-era Mitrophyllum, Meyerophytum, Monilaria and Diplosoma.

Mitrophyllum and Meyerophytum still show a strong, if not exclusive, function of trophic leaves of type A, perhaps a primitive character.

In Diplosoma the leaves of type A are used exclusively for the storage of water during the summer rest and not perform the function of photosynthesis, while the leaves of type B have exclusively trophic activity and does not have the ability to retain the water for long.

From these observations it seems that we can

Morphological differences between the four genera belonging to Mitrophyllinae:a - Mitrophyllum, b - Meyerophytum, c - Monilaria, d - Diplosoma.

Figure 1 - Comparison of four kinds of the Sub-Tribes Mitrophyllinae made simultaneously in the middle of winter vegetative stage [a) Mitrophyllum, b) Meyerophytum, c) and Monilaria) Diplosoma] shows a progressive decrease in the volume (and therefore of trophic function) of the leaves of type A, in relation to the leaves of type B, which are the only visible in Diplosoma. The leaves of type A in this kind only fulfill the function of the reserve during the summering, a function that in other genera is complementary to that trophic.

6 – Una straordinaria aizoacea: Diplosoma retroversum Schwantes

conclude that the species of the genus Mitrophyllum are the most similar to the shape of the primordial Mitrophyllinae, from which it would then be passed to Monilaria, in which the present species may thus be more similar to an intermediate form, from which it has since come to Diplosoma, which could be the most recent.

Growing Diplosoma retroversumWhen I bought the seed of D. retroversum in 1986, yet I had no idea how I should behave. I decided to treat it as the end of the Conophytums. That year it was also the first in which, in the month of Decem-ber, I tried to sow Conophytums in quantity.

For sowing was adopted this technique: the seed was placed in a single jar plastic, square, in turn sunk in a compound very peaty in a cassette made of polystyrene with other similar jars where the seminal Conophytums; the whole was then covered with a sheet of polycarbonate. The soil was kept moist with frequent watering for dipping.

Such sowing was carried out in 24 and 25 of De-cember, in a heated greenhouse, at a point where the temperature, overnight, reached 7-10 ° C (in a very close range to the glasses).

Plants were born plentiful, like emerald drops. In spring the leaves faded yellow. Then dried up com-pletely. At the same time, the same thing happened in Conophytums. Seedling of Diplosoma but there was only emptied rests to the surface of the soil. I removed a thin layer of sand discovering what was left of a seedling; I found a small ball about the size of 1-2 mm.

The Conophytums the end of August began to grow, bursting from the seed coat parchment. Diplo-soma became instead a long wait; when already de-spaired of a recovery, in November, the new leaves finally peeked between the gravel.

The next two years saw the plants reach larger and larger. On the 2nd year one of them splitted in two bodies. The same, in January 1989 (three years after planting) finally gave a first, thin and crumpled flower.

I was sorry to have had a single flower, as I feared that the species is self-sterile. With great pleasure, instead of the flower matured a capsule full of seeds. Sown in December 1989, these seeds showed a very high germination rate.

One of the most important characteristics that I have observed in their cultivation, was the large amount of water for the plants if the soil is con-stantly moist during the active phase, the plants are wilting immediately a more or less marked.

But the period which, after all, is a problem for these plants is related to their vegetative activity, but to their rest.

Unlike the thin skin which provide Conophytums, Diplosoma integument differentiates a rather sub-stantial. By the end of the vegetative stage the un-derground portion is coloured brown tannins. Fol-lowing the tissue, before yielding, becomes woody and perfectly opaque to light. In the age-old speci-mens this structure is no longer evident, as the rem-nants of past vegetation form a thick wrapping pa-per to look. By removing the solids from the leaves during the summer pasture, it is possible to under-stand how the plant produces a sort of “plug” even at the height of the seed coat to completely isolate themselves from the surrounding environment. The roots dry up almost completely, leaving him only a short stub. At which point you have to wonder how it can still keep the life inside.

Even Monilaria develops a protective structure for large bodies that remain in vegetative stasis, how-ever they have the growth axis of the shoot, which creates a series of shortened internodes.

Conclusions on the cultivationSince the strong tunic of Diplosoma I thought they were capable of supporting an absence of water very long. During the summer rest I’ve always left the pot with the plants already dehydrated for seven months in the absence of water. I noticed that the attempt to force the vegetative growth by watering the pot before the vegetative activity is initiated can be fatal. Generally, I water only once or two in mid-October, keeping the pots in a low-temperature (10-15 ° C). In the growing period the soil should always be moist. I also adopted a plastic pot to hold moisture longer.

The soil used is typical for Conophytums, with a good proportion of quartzitic sand and gravel and little or no peat. It can also be used calcareous river sand.

BibliographyHARTMANN H.E.K. (1989), Fruit in Mescmbryanthe-

ma, CSJA, 61 (4), pp. 175-9.HERRE, H. (1 197) -The Generate of the Mesembry-

anthemaceae, Tafelberg-Uitgewers Beperk, Cape Town.

JACOBSEN, H. (1974) -Lexicon of Succulent Plants, Blandford Press, Ltd., London.

ROBERTS, M. (1989) South Africa and Namibia: A Study, Brit. Cactus Succ. J., 7 (3), pp. 58-63; ibid., 8 (1), pp. 4-8; ibid., 8 (2), pp. 36-9.4

7 – Una straordinaria aizoacea: Diplosoma retroversum Schwantes