Plants 10-25 dm. Leaves 5-20 cm. Flowers: calyx distinctly beaked at bud apex, glabrous; petals 6-10 cm. Capsules 3-4 cm. Seeds dark brown, papillose. 2 n = 38. Flowering spring-summer (Apr-Aug). Dry washes, canyons; less than 1200 m; Calif. Romneya coulteri shares with Hibiscus lasiocarpos the distinction of having the largest flowers of any plant native to California.