Description from Flora of China
Annual or perennial herbs or subshrubs, unarmed. Raphides present. Leaves opposite or sometimes ternate, without domatia; stipules persistent or deciduous, interpetiolar and fused to petioles and/or shortly united around stem, 2-6-lobed or -setose, with apices of segments or setae usually glandular. Inflorescences terminal, thyrsiform, subcapitate, cymose, or often corymbiform with axes sometimes elongating and becoming racemiform with age, several to many flowered, pedunculate or sessile, bracteate. Flowers sessile or pedicellate, bisexual, distylous. Calyx limb 4-lobed; lobes sometimes unequal. Corolla white, pink, lilac, or violet, funnelform, salverform, or tubular, with shape sometimes differing between long-styled and short-styled forms, lanate inside tube; lobes 4, valvate in bud. Stamens 4, inserted in corolla throat or near middle of corolla tube, included or exserted; filaments short; anthers dorsifixed. Ovary 2-celled, ovules 1 in each cell, pendulous, apical; stigma 2-lobed, exserted or included. Fruit schizocarpous, ovoid to ellipsoid, sometimes laterally compressed and/or didymous, dry, with calyx limb persistent; mericarps 2, ellipsoid, indehiscent, with 1 seed, early to tardily separating from base upward and falling together with or separately from a carpophore, with carpophore variously filiform and basal to comprising entire enlarged septum; seeds medium-sized, oblong-ellipsoid, compressed; testa thin; endosperm fleshy; cotyledons thin; radicle ascending.
Knoxia was revised by Bhattacharjee and Deb (J. Econ. Taxon. Bot. 6(1): 73-96. 1985), who recognized seven species. Then, it was reviewed anecdotally by Puff and Robbrecht (Bot. Jahrb. Syst. 110: 511-558. 1989), who circumscribed it differently and included nine species. The treatment by W. C. Ko (in FRPS 71(2): 3-7. 1999) differed markedly from these others; it did not cite these authors so presumably Ko had not seen their works. In particular, these other authors considered K. sumatrensis to be a wide-ranging, morphologically variable species and included as synonyms of var. sumatrensis two species that were separated by Ko, K. corymbosa and K. mollis. Because it was based on geographically broader studies of more literature and many more specimens from the type regions, Puff and Robbrecht’s taxonomy is used here.
W. C. Ko (loc. cit.: 4) described the fruit as capsules and the seeds as having a thick stipe, but the fruit of Knoxia have more often been described within Rubiaceae as schizocarps with carpophores, as noted here.
Seven to nine species: tropical Asia and Oceania; two species in China.
(Authors: Chen Tao (陈涛); Charlotte M. Taylor)