Annual herbs; stems simple to divaricately branched. Leaves alternate, entire to once or twice pinnate, sometimes palmately lobed, upper ones bracteate, apex spine-tipped. Inflorescences spiny, densely bracted heads. Flowers sessile or subsessile; sepals 4 or 5, more or less unequal, entire or toothed, mostly free but partly united basally by a scarious membrane; corolla 4- or 5-lobed, funnel-shaped to saucer-shaped, lobes with 1 or 3 main veins; stamens equally or unequally inserted in throat of corolla-tube or in sinuses of corolla-lobes, included or exserted, filaments glabrous; ovary 3-celled, stigma entire or 2- or 3-lobed. Capsule 1–3-celled, 3–8-valved, membranous to chartaceous, dehiscence regular or irregular; seeds 1–many per cell, often minutely pitted.
About 30 species, mainly from North America with 1 species from South America; 1 species naturalised in Australia.