|其他摘要||The genus Hemsleya Cogn. a Sino-Himalayan element, is distributed in southern China, and adjacent northern Vietnam, northern Thailand, northeastern India and eastern Nepal. China is the center of modern geographical distribution. Controversial themes still retained unresolved in Hemsleya as follows: (1) whether Hemsleya was a monophyletic group or not; (2) which group was its sister group; (3) whether H. graciliflora built a monotype subgenus or not; (4) the phylogenetic relationships of sections and species within Hemsleya; (5) the relationships of morphologic characters and phylogenesis; (6) how the modern distribution of the genus was formed.
This paper presented the first molecular phylogeny of the genus Hemsleya using nuclear RPB2, ITS, and plastid trnH-psbA, rpl16 and trnS-trnR DNA sequences to reconstruct the phylogenetic relationships among Hemsleya species. Focuses of the study were made to include the sister relationships of Hemsleya, circumscrption of Hemsleya, intrageneric phylogenetic relationships, and biogeography. The major results were summarized as follows:
Morphological characters are most important evidence of identification, classification and taxonomy. Our studies on morphology clarified some morphological characters. Bunchy tubers are ubiquitous in the Hemsleya. Except typical rotatable, bowl-like, and spherical, umbraculiform or patelliform corollas, there are intermediate corolla forms, such as in H. dipterygia, H. delavayi and H. mitrata.
Based on morphological and molecular evidence, it was suggested that Hemsleya could harbor more than 24 species. Consequently, a new species, H. kunmingensis, was discovered and described.
2. Sister group
Subtribe Gomphogyninae is composed of the genera Hemsleya, Gynostemma and Gomphogyne. Analyses of molecular data based on ITS, rpl16 and trnS-trnR sequences revealed that the Gomphogyne was the only sister group of Hemsleya. It did not corroborate the results of previous studies, which it dealt the Gomphogyne and Gynostemma as the sister groups of Hemsleya.
3. Molecular phylogeny
Analyses were carried out based on ITS, rpl16 and trnH-psbA DNA sequences of 25 taxa of Hemsleya and related genera and based on ITS, rpl16, trnH-psbA, RPB2 and trnS-trnR of 25 taxa, respectively. The results showed that the genus Hemsleya was a monophyletic group with two clades corresponding to the two subgenera: Graciliflorae and Hemsleya. Subgenus Graciliflorae only contained a species, H. graciliflora, and the subgenus Hemsleya harbored all remaining species.
The molecular phylogeny was corresponding to Li’s classification in principle. The topologies of molecular phylogenetic tree covered seven natural groups of Li’s classification, while subsection Amabiles was not supported. The phylogeny of Hemsleya correlated well with the geographic distribution of the species. It was suggested that geography, habitat and other ecological factors would predominantly act as vital driving forces in the evolution of Hemsleya.
The molecular phylogeny also revealed the evolution of morphologic characters, thus the character-state transformations can be inferred as follows:
Tracing the corolla on the molecular phylogeny suggested that the membranous patulous radiate corollas were ancestral character in the Hemsleya, and they were evolved towards carnificate bowl-like corollas and carnificate revolute spherical or patelliform corollas. Palmate compound leaves comprising less than 7 leaflets, stems without tubers and seeds with seed-wing represented the ancestral stage in the Hemsleya; on the contrary, palmate compound leaves comprising more than 7 leaflets, stems with tubers and seeds without seed-wing represented the derived stage.
4. Taxonomic revision
A taxonomic revision of Hemsleya was proposed based on analyses of multidisciplinary data. The systematic treatment was generally in agreement with Li’s classification, but subsections Amabiles and Sphaerocarpae were excluded, simultaneous, the new section Chengyihanae was proposed. Meanwhile, the systematic position of some species among sections and subsections of Hemsleya was re-revaluated and rearranged.
Based on the molecular phylogeny and the statistical analyses of the geographical distribution, the modern patterns of the geographical distribution of Hemsleya were discussed. It was proposed that Kangdian ancient landmass was the center of distribution and diversification of Hemsleya, as well as the center of origin. Furthermore, the center of origin was in the east of Kangdian ancient landmass. The genus Hemsleya could be originated at the transition of between Paleogene and Neogene (Oligocene and Miocene).
The relationships of between phylogeny and geographic distribution suggested that vicariance acted as the key role to the evolution of Hemsleya. It was the major driving forces for differentiation and speciation of Hemsleya. At the early stage of evolution of Hemsleya, dispersal acted as the main factors of expanding distributional area. Subsequently, vicariance became the dominant factors. The modern geographical distribution of Hemsleya was the results of dispersal and vicariance, while vicariance was the vital factor at later stage.|