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Rhynchospora is one of the most species-rich genera of Cyperaceae, comprising c. 400 species in 28 sections. Rhyncospora section Tenues is one of the largest sections and one of the most problematic. Because it is morphologically similar to sections Laevinuces , Luzuliformes and Spermodontes , the characters traditionally used to distinguish section Tenues cannot be reliably used to place species into one of these four sections. These four sections are included in the Psilocarya group of Rhynchospora subgenus Rhynchospora with sections Psilocarya and Dichromena. Previous molecular studies of Rhynchospora indicate that species of the Psilocarya group form a clade and are sister to at least some species of the sections being studied here. Since only 11 of the estimated 41 species in these four sections were included in earlier phylogenetic studies, the relationships among these sections remain unclear. To elucidate these relationships, we conducted a molecular phylogenetic analysis for Rhynchospora , based on plastid trnL -F and nuclear ETS and ITS markers, emphasizing species in these four sections. Results show that sections Laevinuces , Spermodontes and Tenues are individually not monophyletic but, grouped together, form a well-supported clade, Rhynchospora section Tenues s.l. Rhynchospora section Luzuliformes is monophyletic but is not a sister clade of section Tenues. [ABSTRACT FROM AUTHOR]

The new species, Rhynchospora belizensis, is described, illustrated, and compared with phylogenetically closely related and morphologically similar species. Rhynchospora belizensis is known only from southern Belize, where it inhabits sunny, very wet, nutrient-poor, peaty ground of graminoid-dominated, gently sloping hillside seepages. It is unique in its combination of great height, aristate scales, achenes with relatively long stipes, and relatively low and faint transverse ridges on the faces. Vulnerable status appears warranted for R. belizensis because only two populations and fewer than 500 individuals are known, all within a small geographic area. DNA sequence data from the plastid marker trnL-trnF and nuclear markers ETS and ITS diagnose a clade of R. belizensis, its sister R. emaciata, and R. junciformis and R. saxisavannicola. Rhynchospora belizensis is the only member of this clade occurring in Central America; all the others are endemic to South America. [ABSTRACT FROM AUTHOR]

Two new species of Rhynchospora section Tenues are described, illustrated, and distinguished from similar species. Rhynchospora chapadensis and Rhynchospora harleyi are both endemic to the campos rupestres (high-elevation rocky meadows) of the Chapada Diamantina, Bahia, Brazil. [ABSTRACT FROM AUTHOR]