Systematics and phylogeographic studies of Berberis L. (Berberidaceae) in the Nepal Himalaya

Abstract

Berberis L. contains more than 500 species, is the largest genus in the Berberidaceae, and is now recognised to comprise Berberis s.s. with simple leaves and compoundleaved species formally ascribed to Mahonia. Because of its sheer size, much basic taxonomy is required in Berberis, and this thesis provides a taxonomic revision for the species found in Nepal, which includes a key, full descriptions, illustrations, phenology, notes on ecology, distinguishing features and distribution maps. Twenty one species are recognised in Nepal, of which two, B. karnaliensis and B. pendryi, are newly described. Nine taxa are lectotypified during this study. Berberis has a mainly Northern Hemisphere distribution, with its main centre of distribution in the Sino-Himalaya. Berberis s.s. extends into South America where it has a secondary centre of diversity. There have been few phylogenetic studies of Berberis, and previous studies were inadequate because they did not use outgroups to root their phylogenies. This thesis provides parsimony and Bayesian analyses of chloroplast ndhF data of 64 accessions of 59 Berberis taxa, rooted using multiple outgroups including Ranzania, the putative sister group of Berberis. The results support the monophyly of Berberis s.l, but compound-leaved Berberis are shown to be paraphyletic. Berberis higginsae, a member of section Horridae, is sister to all other taxa sampled. The ndhF phylogeny, dated using a fossil calibration, indicates the North American origin of compound-leaved Berberis, and the origin of the simple-leaved South American lineages in long distance dispersal events from Eurasia. ITS sequences of 97 accessions of 79 species of Berberis are studied to investigate the origin and diversification of simple-leaved Berberis in Nepal. The Nepalese species are shown to have multiple origins from at least four different colonisations and have subsequently speciated in situ. The diversification of some groups appears to have been triggered by the active uplift phase of the Himalaya during the Miocene. The tendency of phylogenetically close Nepalese species to grow in similar ecological conditions indicates that phylogenetic niche conservatism is evident in Nepalese Berberis species. Chromosome counts for nine taxa of Nepalese simple-leaved Berberis are obtained, of which five taxa are counted for the first time. All the taxa examined are diploids with 2n=28, suggesting that the polyploidy is not an important factor in the diversification of Berberis in Nepal.