Description from Flora of China
Diapedium K. D. Koenig.
Herbs, diffuse, annual, biennial, or perennial [or sometimes shrubs], with cystoliths; young stems ± 6-angled in cross-section. Leaves petiolate; leaf blade margin entire or subsinuate. Inflorescences of cymes in leaf axils or in terminal spikelike thyrses or panicles of thyrses. Flowers subtended by an involucre of several pairs of bracteoles (= cymule); outermost pair equal or unequal in size, usually concealing inner pair(s), calyx, and base of corolla. Calyx deeply 5-lobed; lobes narrow, equal, apex acute. Corolla pink, resupinate 180° by torsion of tube; tube slender, widened apically, limb 2-lipped; lower lip (in upper position) 3-lobed, lobes ascending cochlear in bud; upper lip (in lower position) entire or emarginate. Stamens 2, exserted from mouth of corolla; anthers 2-thecous; thecae unequally inserted to superposed, base muticous; staminodes absent. Stigma 2-cleft. Capsule substipitate or stipitate, 2-4-seeded; retinacula present; placenta with retinacula separating elastically and rising from inner capsule wall at dehiscence. Seeds lenticular, papillate, lacking trichomes.
About 100 species: tropical and temperate regions worldwide; four species (two endemic) in China.
(Authors: Hu Jiaqi (胡嘉琪 Hu Chia-chi), Deng Yunfei (邓云飞); Thomas F. Daniel)