22. Diodia Linnaeus, Sp. Pl. 1: 104. 1753.
双角草属 shuang jiao cao shu
Authors: Tao Chen & Charlotte M. Taylor
Herbs [or sometimes small shrubs], annual or perennial, unarmed. Raphides present. Leaves opposite or sometimes apparently verticillate due to clustered leaves on unexpanded axillary stems, sessile to shortly petiolate, without domatia; stipules persistent, interpetiolar and fused to petioles, sheath truncate to rounded and often membranous, setose. Inflorescences axillary and sometimes also terminal, glomerulate or capitate, few to several flowered, sessile, bracteate or bracts reduced. Flowers sessile, bisexual, monomorphic. Calyx limb deeply 2- or 4-lobed; lobes sometimes unequal in pairs. Corolla white, pink, or pale purple, funnelform or salverform, inside variously glabrous or pubescent; lobes 4, valvate in bud. Stamens 4, inserted in corolla throat, exserted; filaments developed; anthers dorsifixed. Ovary 2-celled, ovules 1 in each cell, axile and attached at middle of septum; stigmas 2, capitate to linear, exserted. Fruit schizocarpous or indehiscent, ellipsoid to obovoid, papery to cartilaginous, bony, or corky, with calyx limb persistent; mericarps (i.e., cocci) 2, indehiscent, with 1 seed, ellipsoid to plano-convex; seeds ellipsoid-oblong, medium-sized, often sulcate to convex on adaxial (i.e., ventral) surface; endosperm corneous; embryo straight; cotyledons broad; radicle hypogynous.
About 50 species: warm temperate and tropical America and Africa, with several American species naturalized in the Old World tropics; two species (both introduced) in China.
Measurements and characters in brackets below are found in plants of other regions and are included here to aid future identifications of these species, which may be introduced more than once in China and have more variation here than currently documented.