Monoecious annual herbs. Leaves alternate, crenate, deeply toothed or lobed. Capitula unisexual, discoid. Male capitula terminal, spherical, many-flowered; phyllaries few, free; receptacular scales present; corolla 5-dentate. Female capitula axillary, 2-flowered; involucre enclosing and surrounding the 2 flowers, covered with hooked bristles; corolla 0; pappus 0. Achenes obovoid or oblong, enclosed in the persistent hard involucre which bears many hooked spines.

Unusual-looking plants, atypical for Asteraceae.