Schoenus rigidus
Schoenus rigidus is a species of sedge endemic to locations near central regions of the southern coast of South Africa.
Description
The inflorescences of Schoenus rigidus and Schoenus schonlandii are similar, but the primary inflorescence bracts of S. rigidus have membranaceous paper-like extensions that are absent in S. schonlandii.Another species similar in form and also having membraneous paper-like extensions on its primary inflorescence bracts is Schoenus selinae; however, the inflorescences of S. rigidus are more laterally branched compared to those of S. selinae.
The southern African Schoenus have a tendency to form hybrids with each other based on preliminary evidence, which partially explains why they can be difficult to identify. It is not yet known whether S. rigidus is diploid or polyploid, and whether it forms hybrids with other closely related species.
Taxonomy
Schoenus rigidus is a species in family Cyperaceae, tribe Schoeneae, which is a clade that includes genera such as Costularia, Gahnia, Lepidosperma, Oreobolus and Tetraria. Other species in the Epischoenus group of southern African Schoenus are likely to be the most closely related species to S. rigidus based on morphological similarities among species.Species from the southern African Schoenus were once included in the genus Tetraria; however, both molecular and morphological evidence suggests that the two genera are evolutionary distinct. To ensure that this group of sedges is monophyletic, the southern African Tetraria were transferred into Schoenus. The southern African Schoenus can be distinguished from Tetraria species in the field by their lack of stem leaves and the absence of reticulate sheaths at the bases of the flowering stems.