Sylvainia, a new monospecific genus within the subtribe Cephalanthinae (Rubiaceae, Naucleeae)

MARÍA FLORENCIA ROMERO; ANA MARIA GONZALEZ; ROBERTO MANUEL SALAS

Plant Ecology and Evolution

Societe Royale de Botanique de Belgique

Año: 2023 vol. 156

2032-3913

Background and aims – The genus Cephalanthus belongs to the tribe Naucleeae together with 26 other genera. Membersof Cephalanthus mainly grow in temperate and subtropical wetlands in the Americas and Asia, but there is a singleAfrican species that is associated with forest margins and rocky outcrops in moist temperate grasslands. The genuscomprises six species and was historically known to have species with a markedly disjunct distribution: three species arefrom the Americas: C. glabratus, C. occidentalis, and C. salicifolius; two species are from tropical Asia: C. angustifoliusand C. tetrandrus, and one species is from tropical Africa: C. natalensis. Recent molecular phylogenetic studies havesupported the monophyly of the genus, however, most of the morphological synapomorphies are absent in the onlyAfrican species, which is sister to the remaining species of the genus. This work aims to provide a short taxonomicrevision of the genus Cephalanthus, taking into consideration morphological aspects previously underestimated or notconsidered, and to describe a new monospecific genus based on comparative morphological analysis.Material and methods – Vegetative and reproductive material from all the species of Cephalanthus were analysedfollowing conventional taxonomy techniques.Key results – We transferred C. natalensis to a new genus, Sylvainia. Morphological similarities and differences betweenCephalanthus and the new genus are discussed. Cephalanthus glabrifolius, a poorly known species and previouslyconsidered a synonym of C. tetrandrus, is resurrected as a valid species, bringing the number of species in Cephalanthusto six again. All species are described, illustrated, and their known distributions plotted on regional maps.Conclusion – The subtribe Cephalanthinae now has two genera, its type Cephalanthus with six species, and a newmonospecific genus Sylvainia endemic to south-eastern Africa. Based on the amended description of Cephalanthus, nowabsent from Africa, the generic concept is substantially modified, being represented now by three American and threeAsian species.