Family Description: Monoecious; trees or shrubs. Leaves simple, alternate. Male flowers in catkins or heads; perianth 4- to 7-lobed; stamens 8-20(-40), usually twice as many as perianth-lobes. Female flowers 1-3, surrounded by an involucre of scales (cupule); perianth 4- to 6-lobed; styles 3 or 6. Fruit a 1-seeded nut, in groups of 1-3, surrounded by the accrescent cupule.
Family Description: Monoecious; deciduous trees with alternate, imparipinnate leaves. Male flowers in catkins borne on twigs of the previous year; perianth present or absent; stamens 3-40. Female flowers usually few, borne on twigs of the current year; perianth 3- to 5-lobed. Ovary inferior, unilocular or incompletely 2- or 4-celled; ovule 1. Fruit a drupe or nut.
Family Description: Trees or shrubs with latex. Monoecious or dioecious. Leaves alternate (rarely opposite); stipules caducous. Flowers usually densely spicate, capitate or enclosed in a fleshy, urceolate receptacle. Flowers with 3- or 4-partite perianth. Male flowers with 3 or 4 stamens opposite the perianth-segments. Female flowers with ovary 1- or 2-locular, superior; styles 1(2). Ovule anatropous or campylotropous. Fruit a drupelet often surrounded by the fleshy perianth; drupelets often crowded into syncarps.
Family Description: Trees with scaling bark. Monoecious; flowers arranged in globose, unisexual capitula. Perianth 4- or 6-merous, arranged in 2 whorls. Stamens 4-6, opposite the outer perianth-segments. Ovary superior; carpels 3-6, free, each with 1(2) pendulous, orthotropous ovules.
Family Description: Deciduous trees, rarely shrubs, without latex. Leaves alternate, simple, usually asymmetrical at base. Flowers all hermaphrodite or male and hermaphrodite. Perianth herbaceous; stamens erect in bud. Fruit a drupe or samara.