A Monograph of the Genus Isolepis R. Br. (Cyperaceae)

Abstract

Isolepis R. Br. is a predominately southern hemisphere genus of Cyperaceae. It comprises 69 species which are recognised by having terete spikelets, bisexual flowers that lack perianth segments and the absence of a gynophore. The genus was segregated from the heterogeneous Scirpus L., and there has been much disagreement as to whether Isolepis is distinct or part of Scirpus. The phylogeny of Isolepis is reconstructed using cladistic analysis of morphological and DNA (rbcL, trnL intron and trnL-F spacer) sequence data. Isolepis is sister to Ficinia, and together these form a clade (with Scirpoides) sister to Cyperus sensu lato in subfamily Cyperoideae. The genus Isolepis, as currently delimited, is not monophyletic as some species (e.g. I. marginata) are grouped with the Ficinia clade whereas another species (I. humillima) is closer to Cyperus. The removal of the these species from the genus would make Isolepis monophyletic. Three infrageneric clades observed in Isolepis are recognised as subgenera, namely Isolepis (e.g. L sotacea), Fluitantes (e.g. I. fluitans), and Micranthae (e.g. I. hystrix). In addition, subgen. Isolepis has three well supported subclades, recognised here as sections (i.e. sect. Isolepis, Cernuae and Proliferae). The I. fluitans clade has been considered by some authors as a separate genus, Eleogiton Link, but segregating the clades in Isolepis into genera creates groups with obscure limits and minor delimiting characters. The taxonomy of the genus is revised to determine species limits and nomenclature. A full taxonomic account is presented. Two new species and a new variety are described.