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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.


1 Male flowers 3 in a small dichasium, calyx present; female flowers without calyx; fruit a nutlet, winged; cotyledons flat.   (2)
+ Male flower 1, calyx absent; female flowers with calyx adnate to ovary; fruit a nut or nutlet, wingless; cotyledons thick, fleshy.   (3)
       
2 (1) Female inflorescence conelike; bracts woody, persistent, 5-lobed at apex, each bract subtending 2 flowers; male flower with (1 or 3 or)4 stamens   5 Alnus
+ Female inflorescence spicate; bracts leathery, deciduous, 3-lobed at apex, each bract subtending 3 flowers; male flower with 2 stamens   6 Betula
       
3 (1) Female inflorescence capitulate (a compact cluster of several flowers) or racemose-capitulate.   (4)
+ Female inflorescence racemose.   (5)
       
4 (3) Fruit a nut; male flowers with 2 bracteoles; thecae separate, pubescent at apex; bracts campanulate or forming a tubular sheath   1 Corylus
+ Fruit a nutlet; male flowers without bracteoles; thecae not separate, glabrous at apex; bracts forming a tubular sheath   2 Ostryopsis
       
5 (3) Bracts not saccate; nutlet naked or seminaked; male inflorescence enclosed by buds during winter   3 Carpinus
+ Bracts saccate; nutlet completely enclosed by bracts; male inflorescence naked during winter   4 Ostrya

Lower Taxa


 

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