A New Species of Hedythyrsus (Rubiaceae) with Comments on the Generic Delimitations within African Spermacoceae s. l.

Abstract—

A new Hedythyrsus species from Katanga (D. R. Congo), Hedythyrsus katangensis, is described and illustrated based on classic herbarium taxonomy. The generic placement of the new species was determined by comparing it to African genera of the Hedyotis-Oldenlandia complex of the Spermacoceae s. l. that share the terminal position of the inflorescences and the capsular fruits opening by four valves, i.e. Agathisanthemum, Dibrachionostylus, Hedythyrsus, Mitrasacmopsis, and Pseudonesohedyotis. The new species differs from the known Hedythyrsus species in being geoxylic herbs instead of shrubs, and in having bifid, not multifid, stipules. Within Hedythyrsus katangensis two varieties are recognized. Variety ternifolius is distinguished from the type variety by the position of the leaves (often ternate in var. ternifolius, always opposite in var. katangensis) and the pubescence of stems, ovary, and calyx (scabrous to shortly hairy in var. ternifolius, glabrous in var. katangensis). Following the IUCN red list criteria the species can be classified as near threatened.