Ploidy variation in Buddleja L. (Buddlejaceae) in the Sino-Himalayan region and its biogeographical implications

Abstract

The chromosome numbers of 27 populations of Buddleja, comprising 14 species, were counted. The basic chromosome number of all species was x = 19, confirming previous reports. Different ploidy levels (2n = 38, 76, 114, 228) were observed in these taxa, representing diploids, tetraploids, hexaploids, and dodecaploids, respectively. The chromosome numbers of B. yunnanensis, B. brachystachya, and B. macrostachya are reported for the first time. The tetraploid 2n = 76 is a new ploidy level for B. myriantha. Particular attention was given to B. macrostachya, because of the variation in morphology and ploidy level between isolated populations of this species. Two types of interphase nuclei were recognized: the complex chromocentre type in B. macrostachya and the simple chromocentre type in the other species. Biogeographically, most of the polyploidy in the Asiatic species occurs in the Sino-Himalayan region. It seems to be associated with the uplift of the Himalayan Mountains, the orogeny of this region playing an important role in the evolution of polyploidy in these taxa. © 2007 The Linnean Society of London.