BIOSYSTEMATIC STUDIES ON THE GENUS ISOETES IN JAPAN .1. VARIATIONS OF THE SOMATIC CHROMOSOME-NUMBERS

The somatic chromosome number of three Japanese species of Isoetes, I. asiatica, I. japonica and I. sinensis, was determined in 199 individuals from 49 populations. The chromosome number of I. asiatica was 2n = 22, confirming previous reports. However, I. japonica and I. sinensis displayed a diversity in chromosome number. Six cytotypes, 2n = 66, 67, 77, 87, 88 and 89, were found in I. japonica; 2n = 67, 87, 88 and 89 are new counts in the genus Isoetes. 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 in I. sinensis. The chromosome numbers of I. 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.