Species delimitation in Carex section Rhynchocystis has remained relatively constant through its taxonomic history. The section is currently composed of five species distributed in the Western Palaearctic (C. microcarpa and C. pendula) and subSaharan Africa (C. bequaertii, C. mossii and C. penduliformis). Recent phylogenetic studies revealed that the monophyly of C. bequaertii and C. mossii was not well supported and that C. pendula comprises two divergent sister lineages. To evaluate the taxonomic significance of these unexpected results, we performed a rigorous statistical procedure based on morphometrics. We found morphological support for our molecular background, uncovering (1) characters that reflect the evolution of the group and were overlooked by traditional taxonomy and (2) the overlapping of some previously considered diagnostic characters. Our results suggest five species, but only C. microcarpa and C. penduliformis were supported in their traditional concepts. The two lineages of C. pendula corresponded to two morphologically distinct, biogeographically congruent groups: C. pendula s.s. in the western part of the range and C. agastachys in the eastern part. In congruence with the molecular results, C. bequaertii and C. mossii were weakly morphologically differentiated and thus better treated as subspecies of a single species. We propose a revised taxonomic treatment for the group.
