Karyological observations on dwarf individuals of Pilea brevicornuta Hayata (Urticaceae) growing in the riparian habitat in Amami-Oshima of the Ryukyus, Japan

Cytotaxonomical studies were conducted on Pilea brevicornuta Hayata in the Ryukyu Islands and Taiwan. Karyomorphology of dwarf and creeping individuals growing in riparian habitat of Amami-Oshima Island, which is morphologically distinct from normal individuals growing in forest floor, is the main focus of this report. All of the studied individuals of P. brevicornuta including dwarf ones had same chromosome number of 2n = 24. The karyotype formula is 2n = 24 = 6m + 13sm + 5st for normal individual and 2n = 24 = 6m + 12sm + 6st for dwarf individual. The chromosomes of P. brevicornuta were all small with sizes varying between 0.9 and 3.0 μm. Considering the basic chromosome number in the genus Pilea, 2n = 24 is regarded as diploid based on x = 12. Despite the high variability in morphology, P. brevicornuta had remarkably uniform karyomorphology.