Biosystematic Studies on the Genus Isoetes (Isoetaceae) in Japan. IV. : Morphology and Anatomy of Sporophytes, Phytogeography and Taxonomy

Abstract

Morphological and anatomical characteristics and geographical distribution patterns of Japanese Isoetes are described for each of the cytotypes which were determined in our previous cytological studies. A taxonomic treatment for Japanese Isoetes is given. We recognize six taxa of Isoetes in the Japanese flora: I. asiatica (2x), I. japonica (6x), a newly described species, I. pseudojaponica (8x), a newly described interspecific hybrid, I.× michinokuana (=I. japonica × I. pseudojaponica) (7x), I. sinensis var. sinensis (4x) and a new combination, I. sinensis var. coreana (6x). Isoetes pseudo japonica and I.× michinokuana are endemic to Japan and are characterized by both reticulate megaspores and echinate microspores. Isoetes pseudojaponica should reproduce sexually, while I.× michinokuana is a sterile, heptaploid hybrid. Isoetes sinensis var. coreana differs from var. sinensis in the larger size of its microspores. the longer length of its guard cells, and the structure of its leaves in cross section.