Betulaceae Gray
桦木科 hua mu ke
Authors: Pei-chun Li & Alexei K. Skvortsov
Trees or shrubs deciduous, monoecious. Stipules present, free, often deciduous, rarely persistent. Leaves alternate, simple, petiolate, usually doubly serrate, rarely simply serrate, lobulate, or entire; veins pinnate. Flowers unisexual. Male inflorescence precocious, elongate, pendulous, with numerous overlapping bracts; each bract usually subtending a small dichasium with 1-3 male flowers; stamens as many as and opposite sepals or, if sepals obsolete, then stamens of inflorescence to 20; filaments very short, connate or nearly so; anthers 2-loculed, thecae connate or separate, opening by longitudinal slits. Female inflorescence pendulous or erect, with numerous overlapping bracts; each bract subtending a small dichasium with 2 or 3 flowers; calyx with 1-6 scalelike lobes, or obsolete; petals absent; ovary inferior, 2-loculed; styles 2, free; ovules 2, or 1 by abortion, pendulous from near apex of each locule. Fruit a nut or nutlet, winged or not. Seed 1, with straight embryo and flat or thickened cotyledons, without endosperm.
Six genera and 150-200 species: mainly in Asia, Europe, and North and South America; six genera (one endemic) and 89 species (56 endemic) in China.
Because of evolutionary divergence within the Betulaceae, the family has often been divided into tribes (i.e., Betuleae, Carpineae, and Coryleae) or more recently into subfamilies (J. J. Furlow, J. Arnold Arbor. 71: 1-67. 1990).
Li Pei-chun & Cheng Sze-hsu. 1979. Betulaceae. In: Kuang Ko-zen & Li Pei-chun, eds., Fl. Reipubl. Popularis Sin. 21: 44-137.
