BETULACEAE 



The Birches 

 Characteristics of the Genus Betula L. 



HABIT. Small to medium-sized graceful trees and shrubs; 

 crown on young trees narrow, pyramidal, symmetrical; branches 

 short and slender, more or less erect on young trees and becom- 

 ing horizontal or pendulous on older trees. 



LEAVES. Alternate; simple; deciduous; mostly ovate to 

 triangular; acute to acuminate; serrate, dentate, or lobulate; 

 deciduous; petioled; stipules fugacious; scarious. 



FLOWERS. Regular; monoecious; apetalous; appearing be- 

 fore or with leaves; staminate in 1-3 clustered, long, pendulous 

 aments produced early the previous season, every bract with 

 3 individual flowers, each of 4 stamens adnate to a 4-parted 

 calyx; pistillate in solitary, small, slender aments appearing 

 on ends of spurlike lateral branches below the staminate flowers, 

 individual flowers naked, in clusters of 3, and subtended by 

 3-lobed bract. 



FRUIT. Small, compressed, laterally winged nutlet; in erect 

 or pendent strobiles; scales deciduous from persistent cone axis 

 at maturity, releasing the nutlets; maturing in fall of first year 

 (one species maturing in spring). 



TWIGS. Slender; round; marked by horizontal lenticels 

 and small leaf scars; spur shoots with paired leaves commonly 

 present on old growth; pith small, round, homogeneous. Win- 

 ter buds: terminal absent, lateral with imbricated scales; twig 

 lengthening by one of upper lateral buds. 



BARK. Smooth, papery (or in Sweet Birch furrowed) ; resinous; 

 marked by horizontally elongated lenticels; often peeling off" 

 in thin, papery layers. 



WOOD. Strong, heavy, and hard; diff'use-porous ; light- 

 colored; some species highly valued for timber. 



SILVICAL CHARACTERS. Mostly fast-growing and short- 

 lived; adapted to planting on poor, sandy or boggy soil; many 

 used for ornamental planting because of handsome foliage 

 and showy bark; lateral root systems. 



GENERAL. This genus contains about 40 species of trees 

 and shrubs scattered through the Northern Hemisphere; the 

 European white birch {Betula pendula Roth.) and especially 

 its cut-leaf, weeping variety {dalecarlica Schn.) are often planted 

 in this country; eleven species are native to North America, 

 7 of which form trees, 



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