Petal evolution and distribution patterns of Epimedium L. (Berberidaceae)

The genus Epimedium as known at present comprises 50 species, in contrast to the 21 species recognized by Stearn in 1938. Its wide and fragmented range from Japan westward to Algeria indicates its antiquity. The species of the genus Epimedium are far from being evenly distributed over Eurasian land. Approximately 80% species of the total species of the genus are now represented in the central_southeastern China. This must be considered as a very high concentration of the number of species for a genus in a relatively not very large area like that of the central_southeastern China. On the other hand, an analysis of the petal evolution seems to indicate that the genus Epimedium has enjoyed uninterrupted evolution only in China. From the above facts, we can see clearly that the central_southeastern China has the credit of being a center of concentration for the species of Epimedium in the North Hemisphere. Epimedium occupies two widely separated regions, in East Asia and the Mediterranean regions; within each region there are extensive areas from which the genus is entirely absent. Despite the wide and discontinuous distribution outlined above, the ecological requirements of the species appear to be much alike. Essentially woodland herbs, the Epimedium plants often grow in the shade of Fagus forest as dominant species of herb layer in East Asia and the Mediterranean land, and its distribution pattern is very similar to that of Fagus in Eurasian land. It is significant that the distribution pattern of Epimedium coincides in many respects with the modern distribution pattern of the Tertiary genus Fagus. It is reasonable, despite the lack of fossil evidence, to suppose that Epimedium had acquired its wide dispersion in the North Hemisphere during the Paleogene if not before the collision of India with the Eurasia plate and the subsequent uplift of the Himalayas increased aridity in Central Asia. This led to its further disjunction.