A taxonomic revision of the Thesium scirpioides species complex (Subgenus Frisea, Santalaceae) near endemic to South Africa

Abstract

Thesium L. is in need of revision and has been identified as a high priority for taxonomic research in South Africa. As part of an ongoing effort to revise the genus, a group of nine morphologically similar taxa from Subgenus Frisea is revised, including three taxa classified by the IUCN as data deficient due to taxonomic problems and one species new to science (T. atratum N.Lombard & M.M.le Roux). Species of the group, referred to here as the T. scirpioides complex, share the following characters: (1) inconspicuous unarmed herbs or suffrutices, (2) scale-like leaves, (3) indeterminate spike-like inflorescences, (4) post-staminal hairs attaching the anthers to the perianth and (5) twisted placental columns. A comprehensive taxonomic revision of the T. scirpioides complex is presented, including an identification key, updated nomenclature and typifications, descriptions, diagnostic characters, distribution maps and conservation notes. Seven species are recognised and two varieties newly synonymised.