Subshrubs or shrubs, large, glaucous, from creeping rhizomes; sap clear. Stems herbaceous above base, branching, leafy, sparsely pilose or glabrate. Leaves alternate, petiolate; blade gray-green, 1-2× pinnately deeply lobed; primary lobes 3-5, lanceolate or ovate. Inflorescences terminal, 1-flowered; bracts present. Flowers: sepals 3, distinct; petals 6, white, obovate, crinkled; stamens many; anthers yellow; pistil 7-12-carpellate; ovary oblong to ovoid, 1-locular or incompletely to completely multilocular by placental intrusion; style absent; stigmas 7-12, flattened, coherent proximally, radiate-ascending, velvety. Fruits capsular, oblong to ovoid, bristly, dehiscing from apex. Seeds many, ovoid, 1.3-1.5 mm, aril absent. x = 19.

Both species of Romneya , closely related and sometimes merged, are cultivated widely in warm regions for their showy, white flowers, which are the largest in the family.