THE ORIGIN AND DISPERSAL OF THE GENUS CLINTONIA RAF (LILIACEAE) - EVIDENCE FROM ITS CYTOGEOGRAPHY AND MORPHOLOGY

Clintonia Raf. comprising five species is disjunctively distributed in eastern Asia, western North America and eastern North America. Referr ing to its cytogeography and the morphological evolution, we suppose t he genus might have originated from eastern Asia before Miocene era of the Tertiary Period, and then dispersed to North America through the Beringia Bridge. Although four of the five species of the genus concen trated in the area, North America is only the secondary diversificatio n centre of the genus. With regarding to the geographical distribution pattern and karyotypic characteristics of the diploid and tetraploid cytotypes in eastern Asia, the tetraploid cytotype might have arisen p olytopically, and at least three independent arising and two dispersal routes can be recognised: 1). raised from the Hengduan mountains of N W Yunnan and SW Sichuan of China and dispersed westward to the Himalay as; 2). raised from the plateau in north-eastern part of eastern Asia and dispersed eastward to the islands nearby and to North America; and 3). newly raised in a restricted area in the Hualong Mountain of Sout hern Shaanxi of China. In North America, the parallel mountain chains in eastern and western parts, the Appalachians and the Coast Range, we re the main regions of diversification and the courses of dispersal fr om north to south. The disjunction of forest vegetation between easter n and western mountains caused by the xerophilization of the central r egion was the main reason of the disjunctive distribution of the genus in North America. Since after the Quaternary glaciation, there is no connection between those species of eastern and western mountains, the earlier dispersal of Clintonia throughout North America must have bee n completed before the glaciation via the forest belt on the North par t of this continent.