Fls perfect or unisexual, us. cymose, often involucrate. Calyx tubular, often petaloid; petals 0; stamens 1 - ∞. Ovary superior, 1-celled; ovule solitary, erect. Fr. a nut-like achene, sts enclosed in persistent calyx-tube, often glandular; embryo large. Herbs, shrubs or trees with simple, exstipulate, us. opp. lvs. About 20 genera, mainly of America.

Herbs, shrubs or trees, sometimes climbing, sometimes spiny. Lvs opposite or subopposite, occasionally alternate, simple, exstipulate, entire. Infl. usually cymose, sometimes appearing paniculate, rarely fls solitary, often surrounded by coloured bracts; fls ☿ or unisexual, actinomorphic. Calyx tubular, often petaloid, (3)-5-(8)-merous; lobes valvate or plicate in bud; basal part persistent; apical part caducous; bracts sometimes involucrate and simulating the calyx. Corolla 0. Stamens 1-many, free, or connate at base, hypogynous, often unequal. Ovary superior, 1-locular; ovule solitary, basal; style 1, slender; stigma simple or variously divided. Fr. an achene, sometimes enclosed by the persistent base of the calyx (an anthocarp), or a nut. Seed with little or copious endosperm.