Two new species and a new combination in the genus Pauridiantha Hook.f. (Rubiaceae) from tropical Africa

A morphological study of the monospecific genus Rhipidantha Bremek. from Tanzania leads to its inclusion in Pauridiantha Hook.f.; a new combination, Pauridiantha chlorantha (K.Schum.) Ntore & O.Lachenaud, sp. nov., is therefore published, and a full description of this hitherto little-known species is provided. Two new Pauridiantha species from Atlantic Central Africa are also described and illustrated: Pauridiantha gracilipes O.Lachenaud & Ntore, sp. nov. and Pauridiantha principensis Ntore & O.Lachenaud, sp. nov. The former species is endemic to the Ogooué delta in Gabon, and resembles P. liebrechtsiana (De Wild. & T.Durand) Ntore & Dessein, but differs by the 2-locular ovary, the very long fruiting pedicels (12-18 mm) and the frequent presence of spines on the older stems – the last two characters being unique in the genus. The second species is endemic to Príncipe island, and differs from P. insularis (Hiern) Bremek., from the neighbouring island of São Tomé, by the more ascending secondary leaf veins lacking domatia in their axils, longer pedicels, and glabrous stipules. The conservation status of all three species is evaluated acccording to IUCN criteria: P. chlorantha (K.Schum.) Ntore & O.Lachenaud, comb. nov. is assessed as Endangered, P. gracilipes O.Lachenaud & Ntore, sp. nov. as Critically Endangered, and P. principensis Ntore & O.Lachenaud, sp. nov. as Vulnerable. Finally, Pauridiantha microphylla R.D.Good is placed into synonymy of P. canthiiflora Hook.f.