Cephaelis potaroensis Sandw. in Hook. Ic. Pl. 33: pl. 3300. 1935.
Sandwith (Hook. Ic. Pl. 33: pl. 3300. pp. 3-4. 1935) noted the characters separating this taxon from other species of Psychotria and Cephaelis, in their restricted senses, and indicated that Bremekamp believed that “the absence of bracts and bracteoles, the shallowness of the furrow on the flat side of the pyrene, and the small number of flowers in the inflorescence would justify the creation of a new genus.” There is certainly justification for the consideration of the group to which P. potaroensis belongs to constitute a new genus, the principal and essential differences being those stated for the group as a whole, i e an annulus of dense hairs near the base of the corolla, the possession of a central or intermediate appendage between the stipular teeth on the uppermost sheath of the stipule immediately subtending the inflorescence, the apiculate anthers and suborbicular or ovate-suborbicular stigmas of the long-styled flowers. However, if these characters are considered to be the essential criteria for separating this and related species of the group into a separate genus, one encounters other species of Psychotria or Cephaelis in the restricted sense which may possess one or more characters of the Potaroenses group or overlap in other characters. For example, Cephaelis phaneroneura Standl. from Peru, has most of the characters of the Potaroensis group, and strongly resembles P. potaroensis, but the pubescent zone of hairs of the interior of the corolla tube is located from 1/3 to 1/2 way along the length of the tube instead of near the base. Likewise, P. prancei Steyerm. has an intermediate appendage between the stipular teeth of the uppermost sheath immediately subtending the inflorescence, as in the Potaroenses group, but the individual flowers are subtended by elongated narrow bracts and bracteoles, these lacking in the Potaroenses group. The absence of bracts and bracteoles in the Potaroenses group, however, is shared by a number of other species of Cephaelis-like aspect. Also the possession of a shallow furrow on the flat side of the pyrene in P. potaroensis is a character shared by a number of species of Psychotria and Cephaelis-like taxa, and not a significant one to justify in part the creation of a new genus, as judged by Bremekamp. Likewise, the small number of flowers in the inflorescence, noted as another character by Sandwith of significant generic consideration by Bremekamp, is found in, not only the previous group of P. prunifolia-embirensis-prancei, but in other groups of species with a Cephaelis-like aspect, such as P. spadicea, P. oblonga, and many others. Heterostyly appears to be pronounced in this group and the stigmas are markedly different in the short-styled and long-styled flowers. While the characters of apiculate anthers and suborbicular or ovate-suborbicular stigmas of the long-styled flowers would appear to constitute important new characters to be used for generic consideration, unfortunately the short-styled flowers examined on some of the taxa of the Potaroenses group have non-apiculate anthers and the stigmas have an oblong-elliptic or spathulate-elliptic shape. Such differences between long- and short-styled flowers of the same taxon indicate that stability has not been attained within the Potaroenses group so far as the possession of a uniform anther tip and stigma shape is concerned. Finally, although the presence of an annulus of hairs near the base of the corolla tube interior of the Potaroenses is characteristic of Palicourea in general, unfortunately there are a few species of Psychotria in which the hairs on the interior of the corolla tube are found near the base or are lacking entirely, and a few species of Palicourea, i e P. garciae, P. foldatsii, have the annular ring of hairs situated nearer the middle of the tube rather than towards the base. Nor can the shallowness of the furrow on the flat side of the pyrene be used as a generic character of importance in separating the Potaroenses group from the rest of Psychotria. Not only do some specimens of the same species of the Potaroenses group, such as P. fanshawei (Standl.) Steyerm., vary from the ventral face of the pyrene with or without a groove, depending upon the maturity of the specimen, but also many other species of Psychotria may show only a shallow groove or may lack one entirely.
In view of the above considerations, it is believed that because of overlapping of characters evident in the Potaroenses group with other species of other groups of Psychotria, it is not possible to separate generically the Potaroenses group from the remainder of the genus Psychotria.