Description from Flora of China
Spiraea Linnaeus sect. Physocarpus Cambessèdes, Ann. Sci. Nat. (Paris) 1: 239, 385. 1824.
Shrubs deciduous. Branches spreading; buds small, with several alternate, exposed scales. Leaves alternate; stipules caducous; leaf blade usually 3-veined, margin usually 3-lobed, serrate. Inflorescence a terminal corymb. Flowers bisexual. Hypanthium cupular. Sepals 5, valvate. Petals 5, white or pinkish, slightly longer than sepals. Stamens 20–40. Carpels 1–5, connate at base; ovary 1-loculed. Follicles inflated, dehiscent along both sutures. Seeds 2–5.
About 20 species: mostly in North America, also in NE Asia; one species in China.
(Authors: Gu Cuizhi (Ku Tsue-chih); Crinan Alexander)