Description from Flora of China
Herbs, shrublets, or shrubs, erect. Stems (3 or)4-sided, pubescent. Leaves opposite or sometimes 3-whorled, petiolate or sessile; leaf blade usually pubescent, secondary veins 1-3 on each side of midvein, tertiary veins numerous and parallel, margin entire. Inflorescences terminal, capitate or panicled. Flowers 4- or 5-merous, purple or white, usually bracteate. Hypanthium urceolate or flask-shaped, often setiform tuberculate, stellate appendaged, pectinate tuberculate or with polycylic setiform stellate trichomes on stalks. Calyx lobes linear, lanceolate, or ovate-lanceolate, margin ciliate. Petals obovate or broadly ovate, margin ciliate or not. Stamens twice as many as perianth segments, isomorphic, equal or subequal; filaments shorter or as long as anthers; anthers oblong or oblong-ovate, beak long or short; connective decurrent, base abaxially slightly inflated or shortly spurred and sometimes with 1 or 2 setose, adaxially lengthened tubercles. Ovary half inferior, 4- or 5-celled, ± adherent to hypanthium, apex with a setose ring. Style filiform. Capsule ribbed, middle often contracted, dehiscing at truncate apex by 4 or 5 pores. Seeds numerous, curved (cochleate), small, densely granulate.
The Asian species of Osbeckia were revised by Hansen (Ginkgoana 4: 1-150, pl. 1-20. 1977).
About 50 species: tropical W Africa, tropical and subtropical Asia; five species in China.