Usually monoecious, deciduous or evergreen trees or shrubs. Leaves simple, alternate; stipules present, soon deciduous. Perianth of 4-7(-8-9) tepals. Male flowers on slender catkins or spikes, solitary or in groups; stamens 5 or more; pistillode sometimes present. Female flowers solitary or in groups of 3; staminodes usually present; carpels 3, usually united; ovary inferior with 2 pendulous ovules in each locule; styles 3 or more. Fruit a nut (acorn), surrounded by a cup-like structure, the cupule.