Monographs Details: Psychotria humboldtiana (Cham.) Müll.Arg.
Authority: Maguire, Bassett. 1972. The botany of the Guayana Highland--part IX. Mem. New York Bot. Gard. 23: 1-832.

Cephaelis humboldtiana Cham., Linnaea 4: 136. 1829.

Cephaelis humboldtiana var ornata (M.-Arg.) Standi., Field Mus. Publ. Bot. 7: 427. 1931.

Psychotria humboldtiana var caudata M.-Arg., Mart. Fl. Bras. 6(5): 334. 1881.

Psychotria humboldtiana var ornata M.-Arg., Mart. Fl. Bras. 6(5): 334. 1881.

Specimens from the Maroa and Neblina area of Venezuela have larger corollas (24-27 mm long), and in the Cerro Neblina collection the lobes of the corolla are 5.5-6 mm long with leaves greatly reduced in size (6.5-9 × 2.2-3.2 cm) and ovate in shape. However, they are considered here tentatively as within the normal variation of the species. The variations proposed by Müller-Argoviensis (Mart. Fl. Bras. 6(5): 334. 1881), based on width of leaf-blade, number of lateral nerves of the blade, and length of the apex of the leaf, prove to be merely normal variations encountered within the limits of this taxon. Actually, the variation which does occur within P. humboldtiana is not sufficient to warrant any subdivisions of the species.

From specimens collected at the type locality of Yavita (Williams 13946, 14132, Wurdack & Adderley 42929-A), the number of lateral nerves of a leaf blade is found to vary from 20-24, and the leaf blades vary from narrowly lanceolate (1.2-3 cm wide) to oblong-elliptic (up to 4.5 cm wide), the variation in size and shape encountered even on the same specimen and collection number. Although Müller-Argoviensis describes the typical variation of P. humboldtiana from Yavita, as having 12-14 pairs of lateral nerves, other collections, above cited, from the type locality, yield 20-24 pairs.

Psychotria humboldtiana is somewhat intermediate between the concepts of Cephaelis (with each flower surrounded by two bracteoles and bracts) and Psychotria (with flowers not individually subtended by bracts). In this case, usually only one flower out of several in an individual head is surrounded by two bracteoles, while the other flowers may be found without bracts and bracteoles. Most of the flowers, however, are subtended on one side by a bract, or two flowers may be so subtended. The capituliform-corymbose inflorescence consists of three main involucrate heads each supported by an axis. At the base of the three axes are two larger involucral bracts. The two larger bracts of a head surround 3-5 smaller and narrower bracts which enclose 6-8 flowers within each of the two lateral heads. Within a group of three flowers, the outermost bract subtends the cluster as a whole, the outermost flower of this group being subtended by two bracteoles, but the flower next to it is not at all subtended, while the innermost flower is subtended by one bract. The arrangement of the flowers and their subtending bracts in P. humboldtiana indicates the futility of trying to fit species into Cephaelis or Psychotria arbitrarily, as characters of both generic concepts are present within the same head of flowers.

Psychotria humboldtiana bridges the gap between the group containing P. crocochlamys and P. lupulina and P. capitata, and again shows a tendency toward the Cephaelis trend of the group of species characterized by Psychotria colorata.