Psychotria lupulina Benth. in Hook., Jour. Bot. 3: 229. 1841.
Psychotria nervosa Benth. in Hook., Jour. Bot. 3: 229. 1841.
Psychotria leucophaea Poepp. & Endl., Nov. Gen. & Sp. 3: 33. 1843.
Psychotria lupulina var stipulacea M.-Arg., Mart. Fl. Bras. 6(5): 317. 1881.
Psychotria rudgei Brem., Rec. Trav. Bot. Neerl. 31: 301. 1934.
Cephaelis justiciifolia Rudge, Pl. Guian. 28. pl. 43. 1805, not Psychotria justiciifolia Standi. Field Mus. Publ. Bot. 7: 224. 1931.
The type collection of Psychotria nervosa Benth. differs from that of P. lupulina in having shorter stipular teeth, narrower bracts of the involucre, longer corollas, exserted stamens, more nearly truncate calyx margin with shorter, less conspicuously erose and more symmetric margins, shorter petioles, 5-merous instead of 4-merous flowers, and glabrate to less pubescent peduncle and axes of inflorescence. However, as shown by a large suite of specimens examined, none of these differences are of taxonomic significance with intergradations occurring in all these items.
Bremekamp attempted to separate Psychotria rudgei (new name for Cephaelis justiciifolia Rudge when transferred to Psychotria) from P. lupulina on the following basis: “Leaves lanceolate to elliptic, 7-9 cm × 2.1-3.7 cm. Capitula solitary. Calyx glabrous. 5. Rudgei Leaves elliptic, 14-18 cm × 7-10 cm. Inflorescence usually a cluster of capitula. Calyx ciliate. 6. lupulina".
Examination of material determined by Bremekamp and van de Kamer from U does not show any consistency as regards either shape or relative size of leaves nor in the ciliation of the calyx. Of the eight specimens identified as P. rudgei, three have ciliate calyces. The leaf shape varies from elliptic to lanceolate to ovate, and one specimen, Versteeg 413, shows extremes from lanceolate to ovate. As regards the leaf size, although Bremekamp limits the dimensions in P. rudgei to 7-9 cm long by 2.1-3.7 cm broad, the specimens so determined by him or van de Kamer as P. rudgei range from 7-19 cm long by 2.1-9 cm broad, thus showing no differences in size limits as originally stated by Bremekamp for P. lupulina.
Actually, the variation exhibited by the above specimens show that there are no characters by which P. rudgei (Cephaelis justiciaefolia Rudge) can be separated from Psychotria lupulina. While the calyx margin is generally glabrous and eciliate, many specimens exhibit ciliate or erose-ciliate margins. Likewise, variation may be noted in the glabrity or ciliation of the involucral bracts and in their relative width. In the large suite of specimens of P. lupulina examined, it has been found that the leaves vary from 6-24 X 2-10 cm. Since the Suriname specimens all have the broader type of involucral bracts broadest in the middle and mainly 2.5-5 mm broad and l 1/2-3 2/3 times longer than broad, they fall into the category of P. lupulina subsp lupulina var lupulina. Finally, the character used of solitary capitula for P. rudgei versus a cluster of capitula in the inflorescence for P. lupulina cannot be maintained, as the development and relative expansion of the head of flowers with the advent of maturity affects the general appearance and size of the inflorescence.