The Caucasian Representatives of the Genus Paeonia L.

L.M. Kemularia-Nathadse, Trudy Tiflis. Botan. Sada 1961

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Chapter VI

About the origin and basic ways of evolution of the genus Paeonia L.

When some questions about genus origin are concerned, we could not help reminding of our prominent botanists M. G. Popov, prematurely late, who wrote: "The questions of phylogenesis are most difficult, and answers to them are always hypothetical and easily refutable, especially, as far as small groups of organisms from the genus Eremostachys are concerned, for which we have no paleontologic data at all". At the same time M. G. Popov proposed some ways which might be followed in these cases: "Comprehensive study of the genesis of small groups may be only based on the General botanical-geographical concepts concerning the evolution of flora, as a whole, to which this small group relates. Besides, the ampler volume of the flora is taken into account the more reliable conclusion may be obtained in this case".

So, in order to define stages of the evolution of any angiosperms genus, it is necessary to undertake a retrospective examination of the history of angiosperms flora of the Earth, and after this return to the history pertaining to a concrete case connected with the basic floristic region (realm), and so forth, following down to a province where a genus being studied has its centre of developing (that is, a place where the maximum of morphological polymorphism is attained by it)."

The same thought has been briefly formulated by M. M. Ilyin (1946, 1958): "Phylogenesis and florogenesis are inseparable from each other, forming two aspects of one grandiose process, evolving in accordance with the objective laws of dialectics of nature".

So, a solution of the question about origin and development of the genus Paeonia L. which is typical element of the arctotretiary (M. G. Popov, 1940) or tretiary moderate flora" (A. L. Takhtadjan, 1958), is closely connected with questions about the origin and motherland of the angiosperms moderate flora of the North hemisphere.

There are many very interesting hypothesis referring to these questions, which are contradictory with each other, nevertheless, so it is difficult to accept any of them at present.

A very interesting hypothesis about the origin of angiosperms plants and moderate flora, especially referring to the North Hemisphere, is worked out by A. L. Takhtadjan who considers them having come from the montane subtropical of the Ancient Katazia, which included the territories of contemporary China, Indo-China, the East Himalayas and Japan, as it is well-known.

According to A. L. Takhtadjan, the East Asia is "not only a harbour of tretiary relics, , but also a cradle of the angiosperms plants and moderate flora of Eurasia.

As far as the question about origin and motherland of angiosperms plants is concerned, we are inclined to think that those botanists are more right who admit that the tropical zone with humid forests should have been a cradle of the initial angiosperms plants, from where these plants could have penetrated moderate areas (Hallier, 1912, Irmscher, 1922, 1929, M. I. Golenkin 1925, M. G. Popov 1940). There are no doubts, that the environmental conditions of tropics, especially, humid tropics characterized with the maximal variety of angiosperms plants and abundance of their specific composition, are most beneficial for developing plants.

As to the question about origin of the moderate flora of the North Hemisphere, we think that A. L. Takhtadjan was right supposing that the moderate flora had been originated in the midst of montane subtropical flora "as a result of tretiary orogenesis, mostly moreover, it might have presumably arisen on the territory of not only Katasia, as A. L. Takhtadjan suggested, but far more ample region, and according to A. A. Fedorov, "the tretiary deciduous flora of the moderate type, which is traditionally called the arctotretiary, turgayan, angaridian flora, or, bearing in mind its subtropical origin, the flora of Ginkgo, had arisen not in-the subarctic region and not upon spaces of Angarida and still less within the boundaries of the contemporary East Asia, but upon much more spacious area, expanding to the North and the South from 30° latitude.

All over this space the moderate flora could have formed, having gained its most exuberant development in the tretiary period; and as to its contemporary distribution, it should be considered relic.

It may be concluded, that the East Asia, "where remarkably gradual transitions from the montane subtropical flora to the moderate flora from one side, and to the tretiary flora from another side", are seen so clearly, should be considered not only as a cradle for angiosperms plants and the moderate flora of the North hemisphere , but as a harbour where the process of transmitting from the tropical flora to montane subtropical flora, and from the latter to moderate flora, has been fixed and where most auspicious conditions for preserving this flora exist.

Considering the questions about motherland of the genus Paeonia L., that is a typical element of the "arctotretiary" (M. G. Popov, 1940) or the tretiary moderate mesophyllous (A. L. Takhtadjan, 1958) flora, we are inclined to expand the territory of its motherland, adding to the Ancient Katasia's area the Caucasuse's area from the West, "where even during the cretaceous period abundant subtropical flora existed".

All over this space, in humid forests of the tretiary or even cretaceous periods, the ancestor of contemporary peonies could have been arising that is corroborated by the fact that the South-East Asia and Caucasus are most abundant in ancient species (the section Flavonia).

From this places, along with moderate mesophyllous flora the representatives of this genus might have been propagating in various directions, through Beringia to the North America, were the special endemic section Onaepia with two species had settled, and along the north coast of the Ancient Tetis, mainly through over mountainous ridges, the representatives of the genus could have reached the South Europe and Minor Asia.

The initial ancestor of the genus Paeonia L. is most likely to be represented by us as a shrub or small tree, having been growing in the .tretiary shady mesophyllous forests and having leaves which were simple or parted into broad lobes, monocoloured-green at both sides and bare, with large blossoms having yellowish-greenish or yellowish petals, with long pendent (hanging down) naked fruits and naked ovaries.

In result of changing of natural conditions and in process of the tretiary orogenesis, the initial ancestor of the genus Paeonia L. - Prepaeonia had been undergoing changes also.

As the evolution of angiosperms plants went on, which was reductional in respect to soma, according to Popov M. G., the soma of the ancestor of the genus Paeonia L. had been reducing also, and, as a result, the shrubby peonies had begot perennial peonies, and after this, the process of reduction did not go on; so at present no annual representatives of peonies are available.

The further evolution went on in direction of xerophyllous characters developing, that manifested itself in the dissection of leaf-lobes, the pubescence of leaf-lobes, fruits and ovaries, and appearing of the blue-gray bloom upon leaves; however, since all peonies grow under mesophyllous, conditions, it may be concluded that this branch of evolution was very weak; "These plants are forest or, to the most degree, steppe forms which are slightly xerophylous", as M. G. Popov wrote about this.

On a base of studying morphological characters and the types of habitats of contemporary peonies, we may conclude that the most ancient and closest to tretiary ancestors are the shrubby peonies from the section Flavonia Kem.-Nath.. In result of the reduction of soma, the latter peonies retain the most number of primitive characters ^ which occurring to be ancestral are, as follows: the yellow colour of ovaries and fruits and absence of the pubescence upon ovaries, fruits and leaves.

The section Moutan DC is presented in China and Japan only, and the representatives of the section Flavonia Kem.-nath., grow in the East Asia and Caucasus.

Some representatives of these two sections have characters which indicate at some faint tendency of plants to adapt themselves to more arid conditions and which are as follows: the tomentose pubescence upon fruits and the presence of hairs and blue-gray bloom upon leaves.

A weak attempt to adapt themselves to xeromorphous conditions is evinced by the representatives of the North-American section Onaepia, that manifests itself in blue-gray bloom availed by leaves and their leaf-lobes being incised and pulpy; as to pubescence, both species of the section have naked leaves, ovaries and fruits.

Comparatively more advanced features are availed by the representatives of the last two sections Paeon DC. and Sternia Kem.-Nath. As the downy-fruited species prevail in the section Paeon DC., so from 19 species included into it only 3 species are with naked ovaries and fruits; the area of their growing is most ample, as they grow in the oak forests of Euroasia, Caucasus and the North Africa. From 15 representatives of the section Sternia Kem.-Nath. only one species P. anomala L. with bare, long, lengthened fruits grows upon margins of forests of the East Siberia; all the rest are characterized with coarse pubescence upon small short ovate or oval fruits. Since all representatives of this section are characterized with features witnessing plants tendency to adapt to more arid conditions and being such as the incision into narrow leaf-lobes and the tuber-like root thickenings, these species may occupy steppe and turned-into-steppe zones of Asia, the South and Middle Europe, and Caucasus.

So, it may be concluded, that the evolution of the genus Paeonia L. had been following the mesophyllous line (sect. Moutan, sect. Flavonia, sect. Onaepia and sect. Paeon), and the xerophyllous line, only slightly evinced, had revealed itself in forming steppe species of the Sect. Sternia Kem.-Nath., only.