Description from Flora of China
Aalius Rumphius ex Kuntze; Breyniopsis Beille; Ceratogynum Wight; Diplomorpha Griffith (1854), not Meisner (1841); Synostemon F. Mueller.
Erect shrubs, rarely herbs or climbers, monoecious or dioecious; indumentum of simple or gland-tipped hairs, often absent. Leaves alternate; stipules small, paired, inserted at bilateral base of petiole; leaf blade simple, entire, pinnately veined or rarely obscurely 3-veined from base, petiolate. Flowers smaller, apetalous. Male flowers axillary or cauliflorous, clustered or solitary, rarely in racemelike thyrses or short cymes; pedicels usually bracteolate at base; calyx discoid, cup-shaped, or turbinate, entire or 6-lobed, lobes obscurely biseriate, imbricate, erect, or spreading, margins slightly thick, with a whorl of scalelike adaxial lobes at bases of calyx lobes, rarely absent; petals absent; stamens 3, opposite outer sepals; filaments usually connate into a short cylinder; anthers free, bilocular, thecae 2, extrorse, longitudinally dehiscent; pistillode absent. Female flowers axillary, solitary or paired or with males, rarely inserted at base of male inflorescence; calyx usually 6-parted; sepals biseriate, imbricate, sometimes thickened at fruiting; disk absent; ovary ovoid or depressed globose, truncate or retuse at apex, 3-locular; ovules 2 per locule; styles 3, free or connate at base, much divergent, 2-branched at apex, arms recurved. Fruit a capsule, depressed or ovoid, breaking into 3 2-valved cocci when mature. Seeds not carunculate; endosperm fleshy; cotyledon flattened and broad.
The dividing line between Sauropus and the following genus, Breynia, is for the most part rather clear-cut but there are a few species that seem to mix characters of the two genera.
About 56 species: Mascarenes, India, and Sri Lanka to Indo-Malaysia, Philippines, Indonesia, and Australia; 15 species (four endemic, one introduced) in China.
(Authors: Li Bingtao (李秉滔 Li Ping-tao); Michael G. Gilbert)