Herbs, shrubs or climbers. Leaves alternate, simple; stipules membranous, forming a sheath around the stem (ochreous). Flowers small, regular, bisexual or unisexual. Perianth segments 5–6, in 2 whorls, often greenish. Stamens 4–8, perigynous. Ovary superior, 1-locular, with 1 erect ovule; styles 2–3, sometimes united near the base. Fruit a small angular nut enclosed in the persistent perianth. 43 gen., cosmop., particularly N. hemisphere.