67. Pavetta Linnaeus, Sp. Pl. 1: 110. 1753.
大沙叶属 da sha ye shu
Authors: Tao Chen & Charlotte M. Taylor
Shrubs, small trees, or infrequently subshrubs, unarmed. Raphides absent. Leaves opposite or rarely whorled, usually with bacterial nodules and/or domatia in abaxial vein axils; stipules generally persistent, shortly united around stem, triangular, often aristate, often sericeous adaxially. Inflorescences terminal on principal stems, terminal on reduced lateral stems and appearing axillary, or rarely truly axillary, cymose to corymbiform, many flowered, sessile to pedunculate, bracteate with bracts often fused in pairs. Flowers pedicellate or sessile, bisexual, monomorphic, fragrant, with secondary pollen presentation. Calyx limb truncate or 4(or 5)-lobed. Corolla white to cream [or rarely red], salverform with tube slender, inside glabrous or pubescent in throat; lobes 4, convolute in bud. Stamens 4(or 5), inserted in corolla throat, exserted or included; filaments short; anthers dorsifixed near base, sometimes becoming twisted with age. Ovary 2-celled, ovules 1(or 2) in each cell on axile placentas attached at top of septum; stigma restricted to terminal portion of thickened style, very shortly 2-lobed with lobes erect, exserted. Fruit black and often shiny or infrequently white, red, or blue, drupaceous, thinly fleshy, globose to ovoid, with calyx limb persistent or deciduous; pyrenes 2, 1-celled, each with 1 seed, plano-convex or concavo-convex, papery; seeds medium-sized, ellipsoid, discoid, or plano-convex; testa membranous; endosperm corneous; embryo dorsal, curved; cotyledons leaflike; radicle hypogeous.
About 400 species: paleotropical, widespread in Africa, tropical Asia, Australia, and Pacific islands, apparently absent from Madagascar; six species (two endemic) in China.
Secondary pollen presentation is found in Pavetta (De Block, Opera Bot. Belg. 9: 1-218. 1998; Rout & Deb, Bull. Bot. Surv. India 41: 1-182. 1999). Rout and Deb (loc. cit.) reported synchronous flowering in the Indian species of Pavetta. W. C. Ko (in FRPS 71(2): 25. 1999) described the filaments as ranging from short to prolonged, but that latter condition has not been reported by other authors in Pavetta or Ixora. Ko also described the placentas as sometimes attached to the middle of the septum, but Bremekamp (Repert. Spec. Nov. Regni Veg. 37: 2-11. 1934) said this is incorrect and an old mistake in Pavetta.
Bremekamp (loc. cit.; Repert. Spec. Nov. Regni Veg. 47: 12-28. 1939) recognized three subgenera of Pavetta; the Chinese species all belong to his P. subg. Pavetta, and the other two subgenera are restricted to Africa.
Bremekamp, in general, distinguished Pavetta species more narrowly than many other authors; for example, he (loc. cit. 1934; loc. cit. 1939) reported 42 species for the Indian subcontinent, while Rout and Deb (loc. cit.) recognized only 25 species with the rest of Bremekamp’s names synonymized. W. C. Ko (loc. cit.: 25-30) followed Bremekamp (loc. cit. 1934) closely; in contrast, all the morphological variation found among the Chinese species falls well within Rout and Deb’s (loc. cit.: 114-136) circumscription of P. indica Linnaeus. Bremekamp (loc. cit. 1939) noted that the E Chinese plants previously identified as P. indica were included by him in P. hongkongensis.
In particular, Bremekamp (loc. cit. 1934) considered stem characters to be informative taxonomically in Pavetta, particularly green vs. corky-barked stems, but Rout and Deb (loc. cit.) concluded that these represent different developmental stages rather than differences between species. Bremekamp (loc. cit. 1934) considered the arrangement of the bacterial nodules in the leaves to be taxonomically informative for distinguishing infrageneric groups and sometimes species, but Rout and Deb (loc. cit., as "bacterial leaf-galls") found them to have no taxonomic value and concluded that the nodules vary in shape and number among different leaves on a plant as well as between plants of the same and different species. Bremekamp (loc. cit. 1934) distinguished several species based on leaf shape and size, but Rout and Deb (loc. cit.) included notable variation in leaf size and shape, from relatively very narrow to quite broad, within individual species of Pavetta; Bridson and Verdcourt (Fl. Trop. E. Africa, Rub. (Pt. 2), 619-686. 1988) circumscribed several species similarly to Rout and Deb. Bremekamp (loc. cit. 1934) considered several species of Pavetta to have axillary inflorescences, as did Rout and Deb (loc. cit.), but Bridson and Verdcourt (loc. cit.) considered the inflorescences of the African species at least to be terminal on reduced lateral short shoots, as found in a number of Rubiaceae genera, and to appear axillary but not be truly axillary. Bremekamp (loc. cit. 1934) gave much attention to the arrangement of the inflorescence bracts in Pavetta; his descriptions apply to bracts but not bracteoles, so his characterizations may be misinterpreted if not observed carefully. Bremekamp noted (loc. cit. 1934) that occasional flowers with 5 calyx and corolla lobes are found in most Pavetta species, but the majority of flowers are always 4-merous and the genus best considered to be 4-merous; a similar situation is found in other Rubiaceae genera.
The treatment here follows that of W. C. Ko (loc. cit.), for reference. The key here has been augmented with characters from the descriptions, and the descriptions have been augmented with characters from the available specimens cited by Bremekamp.