Description from Flora of China
Perennial herbs or subshrubs, unarmed. Raphides present. Leaves opposite or whorled, without domatia; stipules persistent, interpetiolar and sometimes fused to petioles, triangular to truncate, multifid or setaceous, with segments often gland-tipped. Inflorescences terminal, cymose, paniculate, or corymbiform, several to many flowered, subsessile to pedunculate, bracteate. Flowers subsessile, bisexual, distylous [or rarely tristylous]. Calyx limb deeply (4 or)5-lobed; lobes sometimes slightly to strongly unequal on an individual flower [sometimes with calycophylls]. Corolla white, pink, red, purple, or yellow, salverform to narrowly tubular with tube prolonged and usually expanded at throat, inside villous in throat; lobes (4 or)5(or 6), valvate in bud. Stamens (4 or)5(or 6), inserted in corolla just below throat, included in long-styled, mid-styled, and homostylous forms or exserted in short-styled form; filaments short to well developed; anthers dorsifixed. Ovary 2-celled, ovules numerous in each cell on axile placentas; stigmas 2, linear, included in short-styled and mid-styled forms or exserted in long-styled and monomorphic forms. Fruit capsular, subglobose to ovoid or obovoid with apex often elongated into conical beak, membranous or leathery, loculicidally dehiscent through apical portion, with calyx limb persistent; seeds numerous, small, angled to subglobose.
About 50 species: widespread in Africa and Madagascar, one species cultivated worldwide; one species (introduced) in China.
(Authors: Chen Tao (陈涛); Charlotte M. Taylor)