Description from Flora of China
Shrubs. Branches terete, usually glandular pubescent. Leaves opposite, petiolate to almost sessile; leaf blade oblong-lanceolate to ovate-lanceolate, secondary veins 1 or 2(or 3) on each side of midvein. Inflorescences axillary and umbellate cymes or umbellate or terminal and cymose panicles; peduncle usually short, rarely long or absent; bracts absent or caducous. Flowers (3 or)4(or 5)-merous, minute. Hypanthium funnelform to funnelform-campanulate, (3 or)4(or 5)-sided. Petals 4, ovate, oblong, or rarely lanceolate. Stamens 4(or 5), whorls equal in shape and length; anthers apically attenuate, curved or geniculate, divergent at base, dehiscence poricidal; connective slightly inflated, not appendaged at base. Ovary inferior, 4-celled; placentation axile, paired. Style filiform, simple. Capsule obscurely 4-furrowed, opening at apex by 4 pores, finally loculicidally dehiscing into 4-valves. Seeds very numerous, cuneate.
The genus was revised by Hansen (Bull. Mus. Natl. Hist. Nat., B, Adansonia 1: 43-77. 1982). Further study is necessary to be confident of the status of Blastus tenuifolius and B. tsaii.
Twelve species: Cambodia, China, E India, Indonesia, Japan (Ryukyu Islands), Laos, Myanmar, Thailand, Vietnam; nine species (seven endemic) in China.