Possible horizontal gene transfer: 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 (Sabiceeae-Cinchonoideae-Rubiaceae), 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 not from mutation but from horizontal gene transfer (HGT) from an Acanthaceae, most likely Barleria, due to their common and perhaps uniquely shared microstructure. We briefly review literature on the control of the transition from simple to stellate hairs and on HGT in plants. Virectaria stellata is found in Forécariah and Kindia Prefectures in the Republic of Guinea. A Virectaria specimen without stellate hairs but otherwise similar to V. stellata was collected in Guinea, about 90 km to the North of the northernmost V. stellata collection. This specimen may represent a possible progenitor of V. stellata. The identification of this specimen requires further study. Virectaria stellata 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).