84. Serissa Commerson ex Jussieu, Gen. Pl. 209. 1789.
白马骨属 bai ma gu shu
Authors: Tao Chen & Charlotte M. Taylor
Small shrubs, usually much branched, unarmed, fetid when bruised, usually with short shoots. Raphides present. Leaves opposite but often crowded and apparently verticillate, decussate, without domatia; stipules persistent, interpetiolar and often fused to petioles, generally triangular to truncate, with 1-8 bristles. Inflorescences terminal on principal stems and/or terminal on axillary short shoots and apparently axillary, capitate and several flowered or reduced to 1 flower, sessile, bracteate. Flowers sessile or subsessile, bisexual, distylous. Calyx limb 4-6-lobed essentially to base. Corolla white to pink, funnelform or tubular-funnelform, inside villous in tube; lobes 4-6, valvate-induplicate in bud, with margins sometimes crisped. Stamens 4-6, inserted in upper part of corolla tube, included or exserted; filaments short to developed, anthers dorsifixed near base. Ovary 2-celled, ovules 1 in each cell, erect, basal; stigma 2-lobed, included or exserted. Fruit drupaceous or tardily capsular, obconic to obovoid, leathery to apparently dry, tardily dehiscent septicidally then loculicidally across top, with calyx limb persistent and often enlarging and becoming spiny; pyrenes 2, 1-celled, each with 1 seed, oblong to obovoid, longitudinally densely ridged.
One or two species: China, Japan, Nepal, Vietnam; one or two species (one endemic) in China.
Puff et al. (Rubiaceae of Thailand, 232. 2005) reported that the fruit of Serissa are dehiscent through an apical operculum, releasing two 1-seeded pyrenes; the fruit of the Chinese specimens studied appear to split across the top and partly down the sides to release the obovoid striate pyrenes through the top or disk portion (i.e., the apical section inside the calyx limb), which may correspond to the dehiscence described by Puff et al. The leaf and flower size and pubescence appear to be widely variable, which probably has fueled the selection that has produced a wide range of cultivated forms. Serissa is widely cultivated in tropical and warm temperate regions for its foliage, both variegated and solid, and showy flowers, including frequently as bonsai plants. Normally the cultivated plants in regions outside the native range do not produce fruit. Puff et al. (loc. cit.) discussed and illustrated some of the numerous cultivated forms, which go under the English name "snowrose."
The number of species of Serissa is controversial. W. C. Ko (in FRPS 71(2): 159-162. 1999) and Puff et al. (loc. cit.) recognized two species, others (Govaerts et al., World Checkl. Rubiaceae; http://www.kew.org/wcsp/rubiaceae/; accessed on 20 Aug 2007; D. Lorence, Fl. Mesoamericana, in prep.) recognize only one species. In general, more robust plants have been included in S. serissoides. W. C. Ko’s treatment is presented here for reference, with the description of S. japonica augmented with characters from specimens; however, some specimens are not conclusively assignable to one of these species.