Nonatelia grandiflora H.B.K., Nov. Gen. & Sp. 3: 422. 1819.
Psychotria obscurata M.-Arg., Mart. Fl. Bras. 6(5): 253. 1881.
Palicourea obscurata (M.-Arg.) Standl., Field Mus. Publ. Bot. 7: 143. 1930.
As compared with P. crocea, the inflorescence of P. grandiflora is much more umbelliform-cymose and broader than high with all or most of the primary branches of the cyme arising from the same or nearly the same portion of the rachis, whereas in P. crocea the primary branches arise at obviously different levels, with the lowest one much lower than and apart from the higher ones. Moreover, the corollas of P. crocea are much shorter.
Müller-Argoviensis described the inflorescence and corolla length of Psychotria obscurata from an immature specimen, as evidenced by other collections of this taxon, with much larger corollas, such as Maguire, Cowan & Wurdack 29349. It should be noted that in bud stage the corolla pubescence may be of a denser type with the minute hairs closer together, as in the isotype of Psychotria obscurata, whereas with the approach of anthesis the corolla pubescence is less apparent and more diffuse on the surface. This latter phase is evident in Maguire, Wurdack & Bunting 29349. The collection of Maguire, Wurdack & Bunting 36727 likewise shoes the same difference in density between bud and anthesis stages. Such differences in density of puberulence have been used to separate Palicourea obscurata from P. grandiflora, but the two cannot be separated on their degree of pubescence density, nor on other characters.