Molecular phylogeny of Japanese Eleocharis (Cyperaceae) based on ITS sequence data, and chromosomal evolution.

ITS sequence data were used to estimate the phylogeny of 24 Japanese Eleocharis species and to make karyomorphological observations on 19 of these taxa. Two major clades were identified in Japanese Eleocharis molecular phylogenetic trees: (1) one including all species of section Limnochloa, and (2) another comprising two sections, Pauciflorae and Eleocharis. Phylogenetic analysis including both Japanese and North American species also shows strong support for monophyly of the Mutatae/ Limnochloa clade. The width of the spikelets in the species Mutatae/ Limnochloa is the same as that of the culms, indicating that the relative widths of spikelets and culms are useful characteristics for classification. Two major clades were supported by karyomorphological data. All taxa of section Limnochloa had very small chromosomes, while sections Pauciflorae and Eleocharis had large chromosomes. The basic chromosome number of sections Eleocharis and Pauciflorae is thought to be x=5. Chromosomal evolution in the genus Eleocharis with diffuse centromeric chromosomes may be caused by both aneuploidization and polyploidization. Our data suggest that a 3-bp insertion near the 3' end of the 5.8S gene is useful for intrageneric delimitations of the genus Eleocharis.