Abstract
1. Ch. Yoshinaganthum (2n=36) is endemic to the region of the River of Naka, Shikoku. This report is on the results of a comparative study on external morphology and karyotypes of samples from its geographical range of distribution. Approximately 300 clones were studied.
2. Typical form (type A) of Ch. Yoshinaganthum grew in the region of up-stream. In the region of down-stream several forms with some characteristics of Ch. indicum (2n=36) were found, and they were classified into two types (B and C). The two types were the segregations of natural hybrids between type A and Ch. indicum.
3. Type A was an autotetraploid, and it might have originated from the diploid species Ch. Makinoi (2n=18).
4. Karyotypes of type B were found to differ from those of type A in a pair of chromosomes which had secondary constrictions, in a pair of the smallest chromosomes of the complement, and in two pairs of chromosomes characterized by translocated satellites.
5. Karyotypes of type C were found to differ from those of type A in two pairs of chromosomes characterized by translocated satellites. Type C has the most stable chromosome complement among the three types.
