Description from Flora of China
Adenia Torrey (1843), not Forsskål (1775).
Herbs or subshrubs, rarely shrubs, without stinging hairs. Stems often succulent. Leaves usually opposite, equal or unequal in pairs, rarely alternate; petiolate, stipules deciduous or persistent, 2 at each node, axillary or rarely interpetiolar [or intrapetiolar], usually membranous, sometimes herbaceous, or papery [or fleshy]; leaf blade 3-veined or rarely pinnately veined, base symmetric or asymmetric, margin serrate, crenate, dentate, or entire; cystoliths usually linear. Inflorescences solitary or in pairs, axillary, glomerules usually forming loose, dichotomous cymes or cymose panicles, sometimes spikes or in dense, globose capitula of unisexual or polygamous flowers (plants monoecious or dioecious); bracts small. Male flowers: perianth lobes (2-)4 or 5, valvate or imbricate, often corniculate near apex; stamens (2-)4 or 5; filaments inflexed in bud; rudimentary ovary small to inconspicuous. Female flowers: perianth lobes (2 or)3(-5), subequal or strongly unequal, in fruit enlarged, when 3-lobed, the abaxial one usually gibbous or boat-shaped, much longer and often with a corniculate appendix near apex; staminodes opposite to segments, scale-like, usually oblong, minute or inconspicuous, in fruit enlarged. Ovary straight, often with oblique apex; stigma sessile, shortly penicillate; ovule orthotropous. Achene usually ovoid, usually compressed or slightly compressed, often oblique, without crested appendix at apex, partly enclosed by persistent perianth. Seeds with scarcely any endosperm; cotyledons broad. x = 8, 12, 13, 15, 18.
About 400 species: worldwide in tropical, subtropical, and rarely temperate regions; 80 species (31 endemic, one introduced) in China.
(Authors: Chen Jiarui (陈家瑞 Chen Chia-jui); Alex K. Monro)