EVOLUTIONARY LINKS OF FAR EASTERN FERNS OF GENUS DRYOPTERIS ADAMS
Olga V. Khrapko
Published in: Biodiversity and dynamics of ecosystems in north Eurasia. Vol. 2. Section “Diversity of the flora and vegetation of North Eurasia”. Novosibirsk, Russia, 21-26 August, 2000. Novosibirsk, 2000. P. 113-115.
On the basis of study of taxonomy, geographical distribution, biological, morphological and ecological peculiarities of the far eastern representatives of the genus Dryopteris we came to assumption about evolutionary links and possible ways of entering of the species into the flora of the Russian Far East.
Far eastern pteridoflora is one of the largest in Russia, containing 98 species. Second biggest genus in it is Dryopteris. At the background of well-studied taxonomy, distribution and morphology (Naujalis, Filin, 1983; Khrapko, 1984) the studies on evolutionary links of the species of Dryopteris genus has not been carried on.
The subject of this study was the Far eastern species of the genus Dryopteris which were named after N.N.Tzvelev (1991) as D. sichotensis, D. crassirhizoma, D. monticola, D. fragrans, D. fragrantiformis, D. goeringiana, D. chinensis and D. expansa . The taxonomic analysis and the analysis of geographical distribution have been made, morphology of above and underground organs of 5 species and their ecological peculiarities have been studied, the ontogenesis and seasonal development of plants have been tracked down. The data for this study we obtained from the herbarium and fixed samples, collected in the different regions of Far East. The alive plants from the collection of Botanical Garden of FEB RAS had also been used. Results of this study had been published in Khrapko (1996).
By the morphological, ecological and a number of other peculiarities the species of genus Dryopteris are related to the several groups, which, in our case, coincide with the sections distinguished by Tzvelev (1991). The section Dryopteris combined D. sichotensis, D. crassirhizoma and D. monticola, the species distributed in the Eastern Asia. These are semievergreen plants growing in the mixed temperate forests.
Primarily V.N.Komarov (Komarov, Klobukova-Alisova, 1931) had related D. crassirhizoma and D. sichotense (under the name D. coreano-montana Nakai) to the group of D. filix-mas Schott. Those species had many common features assuming that the species of this group formerly could have a common ancestor species. Perhaps it was related to the warm temperate climate with even temperature with no well-expressed seasons. The latter is confirmed by the open terminal buds and more expressed, xeromorphism of branches and their evergreenness in comparison with other Dryopteris species. In those ecosystems, where ancestor species was formed, the herb cover perhaps was rich in species and diverse. Therefore it was crucial not only to seize a territory, but also survive on it for a long time. This caused the formation of short, solid and non-branched rhizomes in this species.
The species of the section Fragrantes, such as D. fragrans and D. fragrantiformis are characterized by the short and solid rhizomes, long-living branches, densely covered by pellicles, hairs and glandules. D. fragrans is holarctic species with fragmented range. It is common in the highlands, on the rock exposures and stony taluses. D. fragrantiformis is known in Russia from the Southern Kuril Islands. It was described by Tzvelev (1989). The species is very similar to D. fragrans , differentiating from the latter by the some morphological features. Perhaps D. fragrantiformis had developed from D. fragrans as endemic East-Asian form.
Morphology and peculiarities of biological rhythms (long-living branches, xeromorphism of branches and presence of dense pillicles, hairs and glandules) of D. fragrans gives a proof of the origin of this species in the highlands. Then with the changing of climatic and ecological conditions and with the lowering of the subalpine and alpine vegetation belts the alpine and subalpine species were migrating into the low elevation sites. Rock exposures at low elevation became their refuge till nowadays.
The remaining of viability of branches of D. crassirhizoma during the winter may be considered as atavism, because it doesn't play any significant role - the plants are not able to photosynthesize. The remaining of green branches in D. fragrans gives some advantages: from one hand they serves for protection of the terminal budsfrom the low temperatures a drying, from other hand the plants kept branches green are able to start growth earlier in the spring time, when rocky substrate warming up sooner.
Other species have a few common features and they were related to the different sections. D. expansa is the boreal species representing on the Russian Far East the section Aemulae, which also includes other close to it and widespread ferns: D. dilatata (Hoffm.) A.Gray, D. expansa (CPresl) Fraser-Jenkins et Jenny. Taking into account the morphological and ecological features and the distribution of D. expansa , it's possible to assume that penetration of this species on the Far East is connected with the formation of the boreal floras, the superficial terminal buds, dissected branches and short non-branching rhizome give a basis to assume the origin of species on the mountain slopes under the canopy of mixed forests in the conditions of temperate climate. Biomorphological and physiological features allowed to it to radiate through the whole Earth. Later, during the process of migration and changing of the ranges of vegetation formations, this species became one of the component of conifer forests. The high shade tolerance of the species from the one hand and the evenness of climate under the canopy of conifers from other hand promotes its wide distribution.
D. chinensis included into the section of Aemulae is Eastern-Asian endemic. Unfortunately, following to the literary data we cannot to judge trustworthy about the relation of this species to the its habitats. Although basing on morphological features it is possible to relate this fern to the forest mesomorphic species.
D. goeringiana is also isolated species, differentiating from the others by morphology of rhizomes, which are underground plagiotropic with no well-expressed terminal bud. On a character of distribution D. goeringiana is Eastern-Asian continental species closely related to the broadleaf forests, but also occurring under the canopy of mixed forests. Its biomorphological features suggest the evolutionary advance of this species comparing with other ones. Its origin was perhaps related with broadleaf montane forests in the conditions of temperate climate.
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