Description from Flora of China
Trees, shrubs, or clambering or twining lianas, rarely dioecious, unarmed. Raphides absent. Leaves opposite or occasionally in whorls of 3, with or usually without domatia; stipules persistent or caducous, interpetiolar, entire or 2-lobed. Inflorescences terminal and sometimes also in axils of uppermost leaves, cymose, paniculate, or thyrsiform, several to many flowered, sessile to pedunculate, bracteate. Flowers sessile to pedicellate, bisexual and usually distylous or rarely unisexual. Calyx limb 5-lobed nearly to base, frequently some or all flowers of an inflorescence with 1(-5) white to colored, petaloid, persistent or deciduous, membranous, stipitate calycophyll(s) with 3-7 longitudinal veins. Corolla yellow, red, orange, white, or rarely blue (Mussaenda multinervis), salverform with tube usually slender then abruptly inflated around anthers, or rarely constricted at throat (M. hirsuta), inside variously pubescent but usually densely yellow clavate villous in throat; lobes 5, valvate-reduplicate in bud, often long acuminate. Stamens 5, inserted in middle to upper part of corolla tube, included; filaments short or reduced; anthers basifixed. Ovary 2-celled, ovules numerous in each cell, inserted on oblong, fleshy, peltate, axile placentas; stigmas 2-lobed, lobes linear, included or exserted. Fruit purple to black, baccate or perhaps rarely capsular (M. decipiens), fleshy, globose to ellipsoid, often conspicuously lenticellate, with calyx limb persistent or caducous often leaving a conspicuous scar; seeds numerous, small, angled to flattened; testa foveolate-striate; endosperm abundant, fleshy.
The characteristic large, petaloid calycophylls of Mussaenda are frequently but mistakenly considered to be bracts. Mussaenda is frequently confused with Schizomussaenda; Schizomussaenda can be recognized by its large shrub habit with relatively large leaves and calycophylls, its capsular fruit, and its flower buds with the corollas clavate and rather flat-topped with the acuminate ends of the corolla lobes then bent upward to form an erect appressed group of filaments on the top of the bud.
Several species of Mussaenda are frequently cultivated as ornamentals in tropical regions. Mussaenda philippica A. Richard is apparently the most commonly cultivated species and has numerous cultivar forms; Puff et al. (Rubiaceae of Thailand, 215. 2005) presented photos of several of the cultivated forms. This species is pilosulous to villous throughout, with white to pink flowers and calycophylls and with calyx lobes variously 1 to all modified into calycophylls. Also frequently cultivated are M. frondosa of our flora and M. erythrophylla Schumacher & Thonning of Africa; the latter has pilose to villous pubescence on all organs, including the corollas, and deep red inflorescence axes and flowers, including the calycophylls and the outside of the corolla but excepting the corolla limb, which is creamy white.
In addition to the species treated here, Hooker and Arnott (Bot. Beechey Voy. 265. 1838) reported Mussaenda glabra Vahl from "Loo Choo" in China. Mussaenda glabra was described from the Himalaya and has medium-sized leaves, a climbing habit, petioles 3-15 mm, a corymbiform branched inflorescence, calyx lobes 1-4 mm and deciduous in fruit, corolla tubes 13-18 mm, and corolla lobes 3-3.5 mm; this species is otherwise known from 300-1300 m in India and Bhutan and has not been confidently recorded from China. The name "M. glabra" has been frequently applied in herb. to Chinese specimens of both M. erosa and M. frondosa. Also Henry 8279 from Hainan was treated by C. E. C. Fisher (Bull. Misc. Inform. Kew 1928: 274. 1928) as M. parryorum C. E. C. Fischer, a species otherwise known only from Assam, NE India. This identification seems unlikely, especially given that M. parryorum has not otherwise been reported or treated from China or Indochina, so the Henry specimen will need re-examination. Mussaenda parryorum is included for reference in the key below, based on its protologue, but the species is not otherwise treated here.
H. H. Hsue and H. Wu (in FRPS 71(1): 283-306. 1999), Hutchinson (in Sargent, Pl. Wilson. 3: 395-400. 1916), and some other authors have distinguished Mussaenda species in large part based on leaf shape, ovary length, calyx lobe length, and corolla size, but the consistency and distinctiveness of these characters within species of Mussaenda have been questioned by some other authors. In particular, corolla size is apparently sometimes widely variable among living plants in a population (see comments by Wood, Fl. Bhutan 2(2): 781. 1999), and the flower buds of Mussaenda apparently often open prematurely when collected and thus are shorter than flowers at anthesis (pers. obs.). The calyx lobes and the ovary often elongate after fertilization of the ovary, and the calyx lobes then fall off; thus, fruiting plants are very difficult to identify. Also Hutchinson misidentified several widely distributed sets of Chinese Mussaenda specimens, generating confusion in this group (e.g., he identified Henry 12157 as M. pubescens in spite of its pedicellate flowers with corolla tubes ca. 32 mm, vs. sessile and 11-20 mm in M. pubescens); and he described only the "typical" leaf size and shape of several species although he saw material with more variability. The weakness in some cases of Hutchinson’s characters and species concepts is shown by his simultaneous description in his Mussaenda treatment of two new species that were separated primarily on vegetative features and actually are both based on different specimens of a single distinctive species, Schizomussaenda dehiscens.
As noted below, Mussaenda multinervis and M. decipiens were both described as having capsular fruit and most likely belong in other genera, but which other genus or genera is not yet clear so they are maintained here. The measurements below of inflorescence size do not include the corollas and calycophylls.
About 200 species: widespread in tropical Africa, Asia, Madagascar, and Pacific islands; 29 species (18 endemic, one introduced) in China.
(Authors: Chen Tao (陈涛); Charlotte M. Taylor)