Uncaria includes about 30 species of woody lianas that climb by means of unusual hooked spines (or thorns), which are produced in the axils of the leaves. These are considered to be modified peduncles, and occasional plants have partially curved, unusually long spines that bear a few flowers at their ends. Uncaria is also distinctive in its capitate, globose inflorescences with the sessile flowers closely packed together though not fused to each other. The fruits are rather small ellipsoid to fusiform capsules, which become separated as they mature on expanding basal stipes or pedicels -- thus at first glance the inflorescences appear very different in arrangement from the infructescences. Uncaria is found in both the Old and New World tropics, with two species in the Neotropics, one in Africa and Madagascar, and the rest in Asia (Ridsdale 1978). This genus was transferred to the Cinchoneae by Ridsdale (1978), but Razafimandimbison & Bremer (2001) found both morphological and molecular sequence data supported its previous classification in the Naucleeae. This genus was often treated under the name Ourouparia in older floras but that name is now rejected in favor of Uncaria.
Uncaria plants from Madagascar have been included in the circumscription of U. africana by recent authors (Ridsdale 1978: p. 96; Bridson & Verdcourt 1988: pp. 450-452). Ridsdale recognized three subspecies of U. africana, with two of them confined to continental Africa and the Madagascar plants included in the typical subspecies. Haviland cited the name "Uncaria madagascariensis Baill.", but this is an error: Baillon's name was published as Ourouparia madagascariensis. Haviland also gave an incorrect page number for the publication of Baillon's name. Many subsequent authors (e.g., Ridsdale 1978) have simply copied Haviland's errors, which has led to some confusion.