Biosystematic studies on the genusIsoetes in Japan I. Variations of the somatic chromosome numbers

Abstract

The somatic chromosome number of three Japanese species ofIsoetes, I. asiatica, I. japonica andI. sinensis, was determined in 199 individuals from 49 populations. The chromosome number ofI. asiatica was 2n=22, confirming previous reports. However,I. japonica andI. sinensis displayed a diversity in chromosome number. Six cytotypes, 2n=66, 67, 77, 87, 88 and 89, were found inI. japonica; 2n=67, 87, 88 and 89 are new counts in the genusIsoetes. The plants with 2n=66 were the most frequent (72% of total individuals examined) and were distributed throughout Honshu and Shikoku. The plants with 2n=88 occurred in western Honshu and a limited region in northeastern Honshu where the plants with 2n=77 were also found. In contrast, four cytotypes, 2n=44, 65, 66 and 68, were found inI. sinensis. The chromosome numbers ofI. sinensis were reported here for the first time. The plants with 2n=44 occurred only in Kyushu, while the plants with 2n=66 were found throughout a large area of western Japan.