Description from Flora of China
Shrubs, subshrubs, or vines, unarmed, usually extensively twining, usually with fetid odor when bruised. Raphides present. Leaves opposite or infrequently in whorls of 3 or 4, without or sometimes with (Paederia foetida, P. spectatissima) pubescent domatia; stipules caducous or persistent, interpetiolar, triangular to bilobed. Inflorescences axillary and/or terminal on main stem or often on short lateral stems, thyrsiform, paniculate, cymose, or spiciform, several to many flowered, sessile to pedunculate, bracteate with bracts sometimes enlarged and stipitate [to petaloid]. Flowers sessile to pedicellate, bisexual, monomorphic. Calyx limb (4 or)5(or 6)-lobed [sometimes with calycophylls]. Corolla white, pink, or purple, funnelform to salverform usually with tube very slender then abruptly enlarged shortly above base, inside pubescent in tube and throat, sometimes fenestrate near base; lobes (4 or)5(or 6), induplicate-valvate in bud, with margins often crisped to irregular, rarely shortly trifid at apex. Stamens (4 or)5(or 6), included, inserted at various levels near middle of corolla tube, included; filaments reduced [or sometimes developed]; anthers dorsifixed. Ovary 2(or 3)-celled, ovules 1 in each cell, erect, basal, anatropous; stigmas 2, filiform, included or exserted. Fruit characteristic: dry, drupaceous becoming schizocarpous, globose or compressed globose to compressed ellipsoid, with calyx limb persistent and occasionally becoming enlarged; exocarp dry, membranous to papery, usually drying shiny, at maturity fragmenting; pyrenes ("diaspores") 2(or 3), indehiscent, membranous to leathery, hemispherical to flattened, oblong to ovate in outline, entire to winged, rarely pubescent (P. yunnanensis), sometimes borne on a persistent carpophore; seeds with testa thin; cotyledons broadly cordate; radicle short, hypogeous.
Paederia was studied in detail by Puff and collaborators (in Puff, Opera Bot. Belg. 3: 1-376. 1991). They recognized three subgenera based on corolla morphology and size, anther position, style length, the presence of petaloid bracts, and fruit morphology. Two of their subgenera are found in China: P. subg. Paederia, which is restricted to SE Asia and includes P. cavaleriei, P. foetida, P. pertomentosa, and P. stenobotrya; and P. subg. Alatopaederia Puff, which is found worldwide except continental Africa and includes the remaining Chinese species. Puff (loc. cit.: 207-292) presented a species-level taxonomy of Asian Paederia that differed significantly from that of other authors, including W. C. Ko (in FRPS 71(2): 110-119. 1999). In particular, he recognized fewer species, circumscribed P. foetida more widely, and accordingly synonymized several names. Puff also applied the name P. foetida differently than previous authors, and his conclusions were not adopted in FRPS: he applied the name P. foetida to plants treated by W. C. Ko (loc. cit.: 118-119) as P. scandens, and he included the plants treated as P. foetida by W. C. Ko (loc. cit.: 112-113) in P. cruddasiana. Puff (loc. cit.: 216-220) discussed in detail the confusion of these species and the typification of P. foetida and synonymized P. scandens under P. foetida. The treatment here follows Puff, which is well documented and internally consistent, and thus is distinct from traditional taxonomy of SE Asian Paederia.
The fruit of Paederia are unusual in Rubiaceae: they are drupaceous in structure but dry and tardily schizocarpous with the exocarp fragmenting to expose the two pyrenes, which are the dispersal unit or diaspores, sometimes simply enclosed in the fruit and sometimes borne on carpophores (Puff, loc. cit.: 1-376). Paederia species are best distinguished by fruit characters; determinations of flowering specimens are usually provisional. The corollas of most species of Paederia have a notable size range, sometimes varying by 100-200. Paederia foetida is by far the most commonly collected Asian species of the genus and one of the most commonly collected species of Rubiaceae in China. The descriptions below follow Puff (loc. cit.: 207-292) in describing primarily what he termed the "mid-stem region," i.e., the mature stems below the apical, young region. Inflorescence morphology was used by Puff in part to distinguish species; however, these are indeterminate and in several species continue to grow. In particular, their axes continue to elongate for some time during the flowering period; thus, if inflorescences of different ages are compared these characters can be problematic to interpret. W. C. Ko (loc. cit.: 111) described the anthers as basifixed or dorsifixed, but Puff (loc. cit.) reported them as dorsifixed.
Thirty species: tropical and subtropical Africa, Asia, Madagascar, North America (Mexico), and South America; nine species (three endemic) in China.
(Authors: Chen Tao (陈涛); Charlotte M. Taylor)