Cephaelis prunifolia H.B.K., Nov. Gen. & Sp. 3: 377. 1819; DC. Prodr. 4: 535. 1830.
Cephaelis microcephala Willd. ex R. & S., Syst. 5: 214. 1819.
Psychotria microcephala M.-Arg., Mart. Fl. Bras. 6(5): 351. 1881, not Psychotria microcephala Miq. 1850.
Psychotria microcephala ß tripotamica M.-Arg., Mart. FI. Bras. 6(5): 352. 1881.
Psychotria xanthocephala M.-Arg., Mart. FI. Bras. 6(5): 351. pl. S3, fig. 1. 1881.
This taxon is a noteworthy one, remarkable for its strong resemblance to some of the Compositae because of the awn-like or chaffy, setulose bracts which subtend the flowers, as well as to the outermost bracts in a head which resemble the involucre bracts of some Compositae. Müller-Argoviensis attempted to separate Psychotria xanthocephala and P. microcephala with its var tripotamica on the basis of difference in size of involucre, bracteoles, and fruit. However, such differences, in addition to those of leaf size supposed to exist, break down in the many collections obtained by Irwin et al from the Distrito Federal of Estado Goias where P. xanthocephala was originally collected, and demonstrate that the Brazilian collections of P. xanthocephala cannot be separated from isotype material of Psychotria microcephala var tripotamica examined from K.
There is considerable variability in leaf pubescence and dimensions in this taxon, from the larger leaves of Irwin, Souza & dos Santos 10160 to the smaller sizes (4-6 × 2-3 cm) of Irwin, Souza, Grear & dos Santos 17985, and from leaves with pubescent margins only or with the upper midrib and margins pubescent to those having more pubescence on the lower midrib and lateral nerves. There are also size differences shown in the flower heads and their outermost bracts.
The heads are surrounded by four, foliose involucral bracts free nearly to their base, with two outer longer bracts and two shorter inner ones. Within these bracts are usually five flowers subtended at their base by four detachable, unequal, awnlike, bracts resembling the chaff or pales of compositae. The pyrenes show a deep ventral longitudinal groove on their flat ventral face.