Description from Flora of China
Adenosma Nees (1847), not R. Brown (1810); Asteracantha Nees; Cardanthera Buchanan-Hamilton ex Bentham & J. D. Hooker; Hemiadelphis Nees; Kita A. Chevalier; Nomaphila Blume; Physichilus Nees; Polyechma Hochstetter; Santapaua N. P. Balakrishnan & K. Subramanyam; Synnema Bentham; Tenoria Dehnhardt & Giordano (1832), not Sprengel (1813).
Herbs, annual or perennial, often aquatic or hygrophilous, sometimes with axillary spines, cystoliths present. Leaves sessile or shortly petiolate; leaf blade margin entire, crenulate, or sometimes undulate. Flowers sessile, in terminal spikes or several in axillary clusters; bracteoles present or absent. Calyx 5-lobed. Corolla ventricose; limb 2-lipped, lower lip 3-lobed, upper lip apex shallowly dentate; lobes contorted in bud. Stamens 2 or 4, didynamous (posterior pair similar to anterior pair or smaller); anthers 2-thecous; thecae equally inserted; staminodes 0 or 2. Ovary with 4 to many ovules per locule; stigma entire or 2-dentate. Capsule linear-ellipsoid to narrowly oblong, many seeded; retinacula present. Seeds discoid, covered with long mucilaginous trichomes.
About 100 species: widely distributed in tropical and subtropical regions; six species (one endemic) in China.
(Authors: Hu Jiaqi (胡嘉琪 Hu Chia-chi), Deng Yunfei (邓云飞); Thomas F. Daniel)