Phylogeny and Biogeography of Epimedium/Vancouveria (Berberidaceae): Western North American - East Asian Disjunctions, the Origin of European Mountain Plant Taxa, and East Asian Species Diversity

摘要

Using ITS and atpB-rbcL spacer sequences of 38 (of 55) species of the highly disjunct Eurasian/North African Epimedium and all three species of its western North American sister genus Vancouveria, we reconstructed the phylogeny of these two genera and dated major splits with a molecular clock approach. Epimedium was found to be monophyletic with a stem age dated to between 9.7 and 7.4 million years ago (My). Within Epimedium, almost all sections as recognized in the most recent classification of the genus were found to be monophyletic but subg. Epimedium was found to be paraphyletic in relation to subg. Rhizophyllum. Range formation in Eurasia proceeded as follows: in a first step, the western Himalayan part of the generic distribution area (sect. Polyphyllon) was separated from the remainder, followed by a split between the Chinese distribution area (sect. Diphyllon) and the remainder, the separation of the highly disjunct range of E. pinnatum from the Caucasus plus E. perralderianum from North Africa (subg. Rhizophyllum) and the remainder, and in a last step the separation of the European E. alpinum plus the Turkish E. pubigerum from the range of the genus in Japan, Korea, northeastern China and Far Eastern Russia (sects. Epimedium and Macroceras). These results imply that the European mountain species are not most closely related to taxa in mountain areas towards the east (e.g., Caucasus, Himalayas) but rather to taxa in the Far East. Accordingly, in Epimedium the link between western Eurasia and eastern Asia apparently was not through intervening mountain regions but probably through a more northerly deciduous forest belt which does not exist any longer. The largest number of species of Epimedium is found in China (sect. Diphyllon: 44 species mainly in Hubei, Sichuan and Guizhou provinces). The age of this clade was dated to 0.52 to 0.4 My. This implies that the diversification of this group probably is the result of frequent range shifts in the Quaternary.