Herbs shrubs or trees. Leaves usually opposite. Flowers regular, bisexual or unisexual. Calyx tubular, often petaloid, with 5 (rarely 4) very short lobes; upper part deciduous; lower part persistent around the fruit, the whole referred to as an anthocarp. Petals absent. Stamens 1–many, hypogynous, involute in the bud. Ovary superior, 1-locular, with a solitary basal ovule; style simple. True fruit a nut. 30 gen., warm temp., particularly America.