Mitracarpus semirianus (Spermacoceae, Rubiaceae), an overlooked new species from the “campo rupestre” of Bahia, northeastern Brazil, with notes on Mitracarpus lhotzkyanus

Background and aims – Mitracarpus semirianus, an overlooked new species from the “campo rupestre” of the Chapada Diamantina, in the state of Bahia, northeastern Brazil, is here described and illustrated. Specimens of the new species have been previously identified as M. frigidus or M. lhotzkyanus, with which its distinction is discussed. We also provide an updated description of the latter, with notes on its type specimens. In addition, we comment on the distribution, habitat, and preliminary conservation status of both M. semirianus and M. lhotzkyanus. We also provide an updated identification key to the species of Mitracarpus occurring in Brazil.Material and methods – This study was based on fieldwork collections and observations and analysis of specimens deposited in herbaria. Preliminary conservation status assessments follow the IUCN Red List criteria.Key results – Mitracarpus semirianus differs from M. frigidus and M. lhotzkyanus by its glabrous stems, winged at each angle, wing margin hirsute, glabrous leaf blades, and the oblongoid and slightly compressed seeds, with a smooth longitudinal groove dorsally and an inverted “Y”-shaped groove ventrally. The new species is assessed as Endangered according to the IUCN criteria. Furthermore, it is more likely that Riedel, not Lhotzky, collected the original material of the name M. lhotzkyanus. This species is glabrate, not completely glabrous, presenting a generally strigose indumentum on the stems, stipular sheaths, and leaf blades.