Betulaceae S. F. Gray

(Birch Family)

Trees or shurbs; tannis present; bark smooth to scaly, sometimes exfoliating in thin layers, sometimes with prominent horizontal lenticels. Hairs simple, gland-headed or peltate. Leaves alternate, simple, doubly serrate, with pinnate venation, the secondary veins running into a serration; stipules present. Inflorescences determinate, appearing spicate, forming erect or pendulous catkins (aments), terminal or axillary, sometimes exposed during the winter, solitary or in racemosa clusters, with conspicuous bracts, the staminate and carpellate flowers in separate inflorencences. Flowers unisexsual (plants monoecious), radial, inconspicuous, ussually 2 or 3 (forming a cymose unit) in the axil of each inflorescence bract, also usually associated with variously fused second and third- order bracteolus. Tepals (0-) 1-4 (-6), reduced,+ distinct, sometimes lobed, slightly imbricate. Staments usually (1-) 4 (-6), sometimes appearing to be more due to the close association of the 3 flowers of the cymose unit; filaments short, distinct to basally connate, sometimes divided, pollen grains (2-) 3-7- (poro) porate. Carpels usually 2, connate; ovary inferior, with axile placentation; stigmas 2, running along adaxial surface of styles. Ovules usually 2 per locule, but all except 1 aborting, usually with 1 integument. Nectaries lacking. Fruit an achene, nut, or 2- winged samara, associated with variously fused and developed bract-bracteole complex; endosperm present or lacking.

Distribution and ecology : Widspread in temperate to boreal regions of the Northern Hemisphere, but Alnus extending into South America; species occur in early successional habitats or in wetlands, or as dominant forest trees. Nitrogen fixation occurs in specialized nodules on the roots of Alnus.

Economic plants and products : The nuts of Corylus are edible. Several species of Betula (birch) and Alnus (alder) are important for timber or wood pulp; the latter is also important in land reclamation. Betula, Corylus, Carpinus and Ostrya provide valuable ornamentals.

Betulaceae S. F. Gray

(Keluarga Birch)