Schomburgk’s type specimen, collected at Marawaca, is designated as having been collected from British Guiana on the Kew herbarium label, but according to Dr. Bassett Maguire, the specimen was collected from Cerro Marahuaca in Territorio Federal Amazonas of Venezuela, a region visited by Schomburgk. This agrees with the distributional data of Psychotria crassa, which has been collected from the various sandstone table mountains surrounding Marahuaca, such as Duida, Huachamacari, Yavi, Neblina, and Sipapo. Actually, Marahuaca lies between Cerro Huachamacari and Cerro Duida.
The inflorescence has three main axes usually, but five may be present, as in Koyama & Agostini 7459 from Uaipan-tepui. Usually the inflorescence is thrice trichotomous, but in Koyama & Agostini 7459 it is four times branched. On Mount Roraima is a small-leaved variation in which the leaf-blades are frequently only 2-3 × 1-1.5 cm. However, Steyermark 58758, also from Roraima, has larger leaves up to 5.5 × 2 cm, and the leaves may attain as much as 10 cm long on Uaipan-tepui (Koyama & Agostini 7459) or 11.5 cm long on Chimanta Massif (Wurdack 34069).
This taxon is definitely a shrub, but Standley confused matters by stating in his report (Bull. Torrey Club 58: 478. 1931) that “The description of the plant as a small tree may be incorrect, for usually this species is a small epiphytic shrub. It is sometimes difficult, however, to decide whether an epiphytic shrub really is such or whether it is a tree.” Standley confused this species with the epiphytic taxa (P. pendula, P. aligera, P. guadalupensis and related species) which P. crassa resembles. My own field observations and those noted on labels from other collections indicate that P. crassa is usually, if not always, an independent terrestrial shrub.