Abstract: Chromosome numbers of four species of Isoetes from China are reported. The basic chromosome number in the four species is x = 11. A chromosome number of 2n = 22 was reported for the first time in I. hypsophila Hand.-Mazz. The 2n =22 was also found for l. taiwanensis DeVoI, being consistent with previous report. I. sinensis Palmer from China has a chromosome number of 2n =44, which is different from that reported for I. sinensis Palmer from Japan (2n = 44, 65, 66,68). Another species of Isoetes from the Yunnan-Guizhou Plateau, which had previously been identified as I. japonica A. Br., has been shown to have a chromosome number of 2n = 22, which is completely different from that reported for the latter species (2n= 66, 67, 77, 87, 88, 89). More intensive studies on this new species should be made. Data from cytology and morphology of Isoetes species in China suggest that they may provide valuable clues for a better understanding of the origin and evolution of the genus Isoetes in East Asia.

Key words: Isoetes, Chromosome number, Taxonomical significance, China, East Asia