This species is characterized by its rather robust, glabrous habit; its obtuse to rounded stipules; its shiny, stiff, elliptic leaves with a sharply acuminate apex and moderately to quite well developed petioles; its pedunculate to subsessile, generally pyramidal inflorescences (i.e., with a well developed primary axis); it pedicellate flowers; its shortly developed (ca. 1.2 mm long), denticulate calyx limb; and its rather large (7-9 mm long), yellow to red fruits. This species is circumscribed somewhat arbitrarily here, and probably deserves re-evaluation as to whether more than one species is included when more and more adequate material available. In particular there is veriaton among the plants included here in the degree of development of the peduncle, leaf texture, and fruit size; this variation may be clinal, or may support the separation of additional species. As circumscribed here Psychotria onivensis has been collected on a variety of substrates, including white sand, "ferrolitic" soils, and apparently lateritic soils.

Psychotria onivensis is similar to Psychotria menalohensis, which differs in its generally oblanceolate to obovate leaves that are less sharply acute and in particular its subsessile to sessile flowers; the fruits of Psychotria menalohensis generally develop a stipe as they mature, and can be difficult to separate from the pedicellate fruits of Psychotria onivensis. Psychotria onivensis is also similar to Psychotria anhanjaribensis, which also has pedicellate flowers and fruits but differs in its subsessile, shorter, rounded-corymbiform inflorescences (i.e., with the primary axis not more developed than the other principle axes), and its well developed calyx limb 1.8-3 mm long. Bremekamp originally separated them Psychotria onivensis and Psychotria anjanharibensis mainly by petiole and peduncle length, but both species seem to have more variation in these features than he noted.