Review of Cephalanthus (Rubiaceae), with the segregation of the new African genus Sylvainia

ROMERO, M. F.; GONZALEZ, A. M.; SALAS, R. M.

Misiones

Conferencia; VIII International Rubiaceae and Gentianales Conference; 2023

The genus Cephalanthus belongs to the tribe Naucleeae along with 26 other genera. Members of Cephalanthus grow mainly in temperate and subtropical wetlands in the Americas and Asia, but there is a single African species that is associated with forest margins and rocky outcrops in humid temperate grasslands. The genus comprises six species with a markedly disjunct distribution: three species are from the Americas: C. glabratus, C. occidentalis and C. salicifolius; two species are from tropical Asia: C. angustifolius and C. tetrandrus, and one species is from tropical Africa: C. natalensis. Recent molecular phylogenetic studies have supported the monophyly of the genus, however, most morphological synapomorphies are absent in the single African species, which is sister to the remaining species of the genus. The aim of this paper is to provide a brief taxonomic revision of the genus Cephalanthus, taking into account previously undervalued or unconsidered morphological aspects, and to describe a new monospecific genus based on comparative morphological analyses. Vegetative and reproductive material of all Cephalanthus species was analysed following conventional taxonomic techniques. We transferred C. natalensis to a new genus, Sylvainia, taking into account the morphological similarities and differences between Cephalanthus and the new genus. Cephalanthus glabrifolius, a little known species previously considered synonymous with C. tetrandrus, is resurrected as a valid species, bringing the number of Cephalanthus species back to six. The subtribe Cephalanthinae now has two genera, its type Cephalanthus with six species, and a new monospecific genus Sylvainia endemic to southeastern Africa. Based on the modified description of Cephalanthus, now absent from Africa, the generic concept is substantially modified, being now represented by three American and three Asian species.