Conspectus of Palicourea section Potaroenses (Rubiaceae), with a new species from French Guiana and a new combination

International audienceThe species of Psychotria subgen. Heteropsychotria have recently been transferred to Palicourea, following the results of molecular studies showing that they form a monophyletic group with the latter. This paper presents a conspectus of Palicourea sect. Potaroenses (formerly Psychotria subgen. Heteropsychotria sect. Potaroenses), discusses the characters of the section, and provides a key to the species. A new species recently collected in French Guiana is described and illustrated, and one new combination is included. Methods – This paper is based on direct study of herbarium material from BR, CAY, F, K, L, NY, U and US, and additional type specimens from F, K, MO, P, RB, and VEN were consulted online. Two of the species, including the new one, have also been studied in the field. Common practices of herbarium taxonomy have been applied. Results – Palicourea sect. Potaroenses is characterized by the capitate inflorescences surrounded by an involucre of 4–20 elliptic, yellow to red bracts, the leaves with lateral veins strongly ascending and almost reaching the margin, the long tubular calyx, the unusually long corolla tube for the genus, and the peculiar stipules, consisting of an internal sheath and two interpetiolar pieces connate to the sheath by their central part. The section includes eight species: Palicourea aetantha (Sandwith) Delprete & J.H.Kirkbr., P. fanshawei (Standl.) Delprete & J.H.Kirkbr., P. formosissima (Steyerm.) Delprete & O.Lachenaud, P. phaneroneura (Standl.) Borhidi, P. potaroensis (Sandwith) Delprete & J.H.Kirkbr., P. psittacina (Steyerm.) Delprete & J.H.Kirkbr., P. spectabilis (Steyerm.) Borhidi, and the new species P. aurantiosplendens O.Lachenaud & Delprete. The latter is most similar to P. psittacina, from which it can be separated by the dense patent indumentum of the stems, calyx lobes, and inner side of the bracts, and the smaller size of the latter; it also resembles P. spectabilis and P. formosissima, but differs in having the stipules with four lobes on each side (vs. two), the bracts nearly glabrous outside (vs. densely hirsute on both sides) and the calyx lobes much more pubescent than the tube (vs. the calyx uniformly hairy). It is only known from a small area on the upper Sinnamary River, north-central French Guiana, and is evaluated as Endangered (EN D1) according to IUCN criteria