A rather large family, widely distributed, most abundant in the north temperate zone; herbs, rarely shrubs, with milky, mostly yellow juice and narcotic or acrid properties; the leaves mostly alternate, without stipules; the parts of the flower usually all separate and distinct, borne on a top-shaped receptacle. There are usually two sepals, which fall off when the blossom opens, and usually four petals, overlapping and crumpled in the bud; the stamens are usually numerous and conspicuous, with thread-like filaments; the superior ovary becomes a many-seeded capsule.

There are only two kinds of Romneya, much alike, smooth, stout, perennial herbs, several feet high, with colorless sap, the leaves alternate and more or less divided; three sepals, each with a broad wing on the back; six, large, white petals; many stamens; the ovary covered with bristles. These plants are nowhere common, but are found from Santa Barbara south, and in lower California sometimes grow in great profusion. They are extensively cultivated and much admired abroad.