Evea tontaneoides Britton & Standley, Jour. Wash. Acad. 13: 106. 1923.
Cephaelis tontaneoides Standl., Field Mus. Publ. Bot. 8: 183. 1930.
Cephaelis tontaneoides (Britton & Standley) Williams & Cheesman, Fl. Trin. & Tob. 2(1): 41. 1928.
The type collection of Evea tontaneoides represents a broad-leaved extreme of the normal narrower type usually encountered in P. callithrix var tontaneoides. The leaves in the type collection of Evea tontaneoides are up to 2.6 cm broad and have a different shape (ovate or oblong-ovate instead of lanceolate or linear-to oblong-lanceolate), and only twice as long as broad, instead of 3-4 1/2 (rarely 2 1/2) times longer than broad as in the average collection of P. callithrix var tontaneoides. However, the type collection of Evea tontaneoides shows the characteristic pubescence of the var tontaneoides, with a soft abundant pilosity on the lower leaf surface together with an abundance on the upper leaf surface of short appressed to ascending cilia.
In typical P. callithrix var callithrix the leaf pubescence of the upper surface is sparse or absent, except along the midnerve, as shown by the specimens of Oldeman & Sastre 48 and 98 from French Guiana.
The flowering heads of P. callithrix are subtended by two larger outer bracts which surround 11-13 somewhat smaller interior bracts, which are raised on a slightly higher level. About 14 flowers are contained within a single head, with usually 4-5 flowers occurring on each of the usually three axes of the inflorescence. These flowers are usually subtended by a single bract, but frequently three bracts (a single bract and two bracteoles) are present at the base of an individual flower. Sometimes two bracteoles subtend a single flower or two bracteoles may be situated on either side of two flowers. In a terminal group consisting of four to five flowers, the outer flower is found to be subtended by three larger bracts at its base, while another three flowers are subtended by a total of three bracts at their base, one of the three bracts subtended by two bracteoles, but the other two flowers are not subtended by bracteoles. Such an arrangement illustrates the non-uniformity often encountered in species casually judged as “Cephaelis” types, and why it is impossible to draw any hard and fast lines to delimit either that genus or any other one arbitrarily separated from Psychotria on characters based on the flowers being subtended by two bracteoles.