Type. Selva tupida de rebalsa, raudal Trapichote, Delta del Ventuari, Amazonas, Venezuela, alt 126 m, 20 Apr 1942, Llewellyn Williams 14983.
This species has the leaves opposite instead of in three’s as in P. coussareoides Standi, or P. tillettii Steyerm. Vegetatively, it may be distinguished by the presence of domatia in the lower axils of the leaves and the enlarged nodular areas at the upper axils, these not present either in P. coussareoides or P. tillettii. Other distinguishing characteristics are that the greatest breadth of the leaf blades is at or below the middle in P. ventuariana, but mainly broadest above the middle in P. coussareoides, giving the latter a more oblanceolate or obovate shape; also the apex of the leaf blade in P. ventuariana is long cuspidate or acuminate, whereas those of P. coussareoides are only shortly acute or obtuse with the acumen 0.5-1 cm long. The ovary in P. ventuariana is definitely 2-celled with a strong septum separating the two cells and with one ovule arising from the base of each cell, as characteristic for Psychotria. Psychotria ventuariana is remarkably similar to Coussarea leptophragma and often confused. For example, the specimen of Breteler 4042, although possessing strongly 2-celled ovaries, has the young fruit showing only one seed and is identical with Ewel 117 from the Brazilian side of Cerro de la Neblina. Domatia, however, are present in the Breteler collection, but absent in the collections of Ewel 117 and 118. Domatia are present in the other collections noted for Coussarea leptophragma, as in Spruce 2810 and Holt & Gehriger 358.
In the type collection of Coussarea leptophragma the flowers are all pedicellate and the calyx tube has four shortly subulate teeth, and the corollas are large and 4-lobed. On the other hand, in the type collection of Psychotria ventuariana the flowers are all sessile and pentamerous, with 5 stamens, 5 corolla lobes, and 5 calyx lobes, and the calyx lobes are broadly triangular and not subulate. The Ewel 117 and 118 specimens possess shallowly 5-lobed blunt calyx lobes, but differ from the Breteler 4042 collection in having different stipules in which the 2 rigid teeth extend like ribs just below the apex of the stipular sheath to the middle of the apical center, and in showing remains of the congested flower bases at the ends of the floral axes, thus resembling the little groups of flowers crowded in P. boliviana and P. tillettii. On the specimen of Ewel 118 in the Maracay herbarium, the fruits are 2-seeded and seem best to fall under P. podocephala, and, because of the sessile fruits, 5-lobed calyx with short and broad lobes and clusters of remains of flowers cannot be identified with Coussarea leptophragma. The specimen of Ewel 117, previously identified as Coussarea leptophragma, lacks domatia in the leaf axils. It has both 1- and 2-seeded fruits, and seems to fit best in Psychotria boliviana.
Breteler 4042, on the other hand, with sessile but not aggregate flowers (as in Ewel 117 and 118), is closest to Psychotria ventuariana, having domatia and similar stipules (unlike those of Ewel 117 and 118), but the fruit in early maturity has aborted to only one fertile cell, the other cell being empty. In the fruiting collection of Steyermark 58013 of Psychotria coussareoides the fruit is 2-seeded with a definite septum.