Annual or perennial herbs, the stems erect or twining. Leaves opposite or sometimes alternate, toothed, lobed, or divided, petioled, the stipules persistent. Flowers dioecious; staminate flowers in panicled racemes, usually 5-parted; pistillate flowers in bracted spikes, the perianth entire, the ovary 1-celled, the styles or stigmas 2, the ovule pendulous. Fruit an achene, with crustaceous pericarp. Endosperm fleshy; embryo curved or coiled.