Psychotria quadrifolia Rudge, Pl. Guian. 1: 27. pl. 42. 1805.
Palicourea umbellata DC., Prodr. 4: 526. 1830.
Uragoga quadrifolia (Rudge) O. Kuntze, Rev. Gen. 2: 962. 1891.
De Candolle placed P. quadrifolia Rudge in a section of Palicourea with “floribus panicularis” as opposed to “floribus corymbosis cymosisve” for P. umbellata, at the same time describing P. quadrifolia as having “corymbis multifloris.” Actually, Rudge’s description of Psychotria quadrifolia (“flores numerosissimi in corymbum amplum terminalem dispositi”), supplemented by his plate 42, especially of the habit, explicitly brought out the corymbose type of inflorescence.
Both Palicourea umbellata DC. and Psychotria quadrifolia were collected originally from British Guiana. A comparative study of these taxa indicates that they are conspecific, sharing glabrous tetragonous stems, glabrous acuminate leaves in verticils of 3-4, and corymbosely disposed, widely spreading inflorescences with glabrous branches.
On Rudge’s plate and in his description the calyx teeth are described and depicted as acute. Actually, they are inconspicuous and shallow, suborbicular, rounded protuberances. The two subtending linear or subulate bracts at the base of the sessile flowers often project above the calyx and resemble calyx teeth if not viewed carefully. In Palicourea umbellata these subtending bracts are prominent and up to 2-3 mm long.
Kew Index incorrectly ascribed the combination “Palicourea quadrifolia” to Rudge. Actually, Rudge published this taxon under Psychotria (Pl. Guian. 1: 27. pl. 42. 1805).