Abstract
Intraspecific polyploidy and cytogeography were clarified in the samples of Houttuynia cordata (Saururaceae) studied in the Sino-Japanese region of eastern Asia, ranging from Nepal, China, northern Thailand, Taiwan to Japan. Five chromosome numbers of 2n=72, 80, 96, 112 and 128 were detected, four of which were firstly recorded here. These chromosome numbers suggested that the basic chromosome number of Houttuynia could be x=8. The observed cytotypes were evaluated as 2n=72, 80, 96, 112 and 128, and represented 9x, 10x, 12x, 14x, and 16x, respectively. The continental part of east Asia harbored intraspecific polyploidy ranging from 9x to 16x, and only one cytotype of 12x or 2n=96 was found from the eastern edge of the Asian continent between Taiwan and Japan. The evolution of basic chromosome number was discussed based on a phylogenetic tree of the Saururaceae, suggesting that x=11 was an archaic basic chromosome number in this family. Houttuynia may have experienced a disploid reduction from x=11 to x=8, as an autoapomorphy and subsequent intraspecific polyploidization in continental eastern Asia.
