The phylogeny of Isolepis was investigated by cladistic analysis of rbcL and trnL-F sequence data from 69 species in 26 genera of Cyperaceae. The genus Isolepis, as currently circumscribed, is not monophyletic. Three species, I. nodosa, I. Marginata, and I. trolli, are more closely related to Ficinia, whereas the position of I. humillima is uncertain. The remainder of Isolepis is sister to Ficinia and Desmoschoenus and together with Hellmuthia and Scirpoides form a clade sister to Cyperus s.l.; this clade shares the Cyperus-type embryo. Scirpus s.l. is not monophyletic. Scirpus s.s. and other genera with a Fimbristylis-type embryo form a monophyletic clade, whereas Schoenoplectus and other genera with a Schoenoplectus-type embryo form a grade.
Communicating Editor: James R. Manhart