Description from Flora of China
Shrubs, small trees, or rarely vines twining and/or climbing by adventitious roots (Psychotria serpens), [infrequently dioecious or polygamo-dioecious], unarmed, tissues and/or pubescence often drying dark gray or dark reddish brown. Raphides present. Leaves opposite or rarely in whorls of 3 or 4, often with foveolate and/or pubescent domatia; stipules caducous or infrequently persistent, interpetiolar or sometimes shortly united around stem, entire or 2-lobed, rarely with lobe glandular, inside (i.e., adaxially) at base with well-developed colleters, these usually persistent after stipule falls, usually drying red-brown. Inflorescences terminal often becoming displaced to pseudoaxillary or rarely axillary, cymose, corymbose, paniculiform, glomerulate, or capitate, several to many flowered, sessile to pedunculate, bracteate with bracts sometimes reduced or sometimes enlarged or involucrate. Flowers sessile to pedicellate, bisexual, usually distylous [or infrequently unisexual]. Calyx limb (4 or)5(or 6)-lobed. Corolla white, yellow, or flushed with pink, funnelform to tubular, inside glabrous or variously pubescent, lobes (4 or)5(or 6), valvate in bud, sometimes abaxially with thickenings or horns near apex. Stamens (4 or)5(or 6), inserted in corolla tube or throat, usually included or partially exserted in long-styled flowers and exserted in short-styled flowers; filaments short to developed; anthers dorsifixed near base. Ovary 2-celled, ovules 1 in each cell, basal; stigmas 2, linear to subcapitate, usually exserted in long-styled flowers and included in short-styled flowers. Fruit red, orange, or infrequently white (P. serpens), purple (P. manillensis), or black (P. cephalophora, P. straminea), drupaceous, fleshy, ellipsoid, ovoid, or subglobose, with calyx limb persistent or infrequently deciduous, with pedicels or stipitate base sometimes elongating; pyrenes 2, 1-celled, each with 1 seed, plano-convex, bony, on dorsal (i.e., abaxial) surface smooth or longitudinally ridged, on ventral surface smooth or longitudinally sulcate; seeds medium-sized, ellipsoid to plano-convex, with testa thin; endosperm fleshy or corneous, sometimes ruminate; embryo small, basal; cotyledon flat.
The genus Cephaelis was separated from Psychotria by numerous authors in the 19th and first part of the 20th centuries, based on inflorescence form: Cephaelis included species with capitate inflorescences with enlarged, often involucral bracts, vs. branched inflorescences with smaller bracts in Psychotria. However, it is now clear that this inflorescence arrangement has arisen far more than once within this group and that "Cephaelis" actually included a polyphyletic set of species that are more closely related to various other species of Psychotria than to each other. Consequently, recent authors (e.g., Steyermark, Mem. New York Bot. Gard. 23: 443-717. 1972; Taylor, Opera Bot. Belg. 7: 261-270. 1996) have formally synonymized Cephaelis with Psychotria.
A recent treatment of Psychotria in the Philippines (Sohmer & Davis, Sida, Bot. Misc. 27: 1-247. 2007) does not consider any species or names outside its study area but includes some Chinese species that occur in that region. However, these authors have a partially different species concept and morphological interpretation of inflorescence characters from C. M. Taylor, so their work is not completely comparable to the treatment here.
About 800-1500 species: tropical and subtropical Africa, America, Asia, Madagascar, and Pacific islands; 18 species (five endemic) in China.
(Authors: Chen Tao (陈涛); Charlotte M. Taylor)