Trees. Leaves alternate, unequal at base; stipules scarious, soon deciduous. Flowers generally hermaphrodite or partly also unisexual, yellowish-green, arising from one-year-old twigs, arranged in fascicles and appearing before leaves. Perianth more or less campanulate, marcescent, of (3-) 5 (-9) segments. Stamens as many as segments; filaments inserted at base of perianth, later exserted. Ovary usually 1-celled, compressed, with short style and 2 pubescent stigmas. Fruit a compressed samara, notched at tip of wing. Seeds with straight embryo and without endosperm.