Virectaria stellata (Sabiceeae Rubiaceae), a new sandstone cliff species from the Republic of Guinea with stellate hairs recorded for the first time in the Rubiaceae

Virectaria is a morphologically isolated genus of tropical African herbs or subshrubs, occurring from Senegal to Tanzania. Virectaria stellata, a new species from Guinea, is published. It is a perennial herb, with stems becoming creeping and rooting, to 60 cm long. Virectaria stellata has stellate hairs, recorded here for the first time in the family Rubiaceae. We hypothesize that the stellate hairs of this species result from horizontal gene flow from an Acanthaceae, most likely Barleria, due to their common and perhaps unique microstructure. Virectaria stellata is found in Forecariah and Kindia Prefectures in the Republic of Guinea. The species occurs in fissures in vertical sandstone rock at altitudes of 450 to 910 m, in sun or half-shade. An overview of sandstone endemic plant species in the vicinity of the new Virectaria is provided. No threats have been observed, therefore, Virectaria stellata is provisionally assessed here as Least Concern (LC).