Betula pendula Roth - Silver birch, weeping birch.
Taxonomic position.Family Betulaceae S.F.Gray, genus Betula L.
Synonyms.Betula ajanensis Kom., B. cajanderi Sukacz., B. demetrii Ig.Vassil., B. ellipticifolia V. Vassil., B. grandifolia Litv., B. insularis V.Vassil., B. mandshurica (Regel) Nakai, B. platyphylla Sukacz., B. platyphylloides V.Vassil., B. pseudopendula V.Vassil., B. sajanensis V.Vassil., B. talassica Poljak., B. tauschii (Regel) Koidz., B. tiulinae V.Vassil., B. transbaicalensis V.Vassil., B. uschkanensis Sukacz., B. verrucosa Ehrh., B. vladimirii V.Vassil.
Morphology and biology.Deciduous tree up to 25 m tall with pendulous branches. Young shoots reddish-brown, slender, glabrous, with light convex glands. Trunk bark snow-white, flaking off in thin layers; trunks of old trees with deep black fissures at the base. Leaves 3-8 cm long and 2-6 cm wide, triangular-ovate to rhomboid, elongately cuspidate, doubly serrate-dentate at margins, tough, with resinous glands, young ones glossy and viscous. Monoecious plant with unisexual flowers aggregated in catkins. Male catkins drooping, located 2-3 at branch ends. Female (pistillate) catkins solitary at the ends of leafy lateral branchlets. Floral scales with deflexed, or less often, slightly ascending broad lateral lobes, shortly pubescent, ciliate at margin. Fruit a winged nutlet, its wings being 2-3 times as wide as the nutlet. Very polymorphous species, creating a great range of forms different in color and structure of leaves, floral scales, nutlets, crown shape.
Anemophilous. Anemochore. Propagates by seeds. Seeds are best planted in autumn or early spring. When planting in spring, the seeds should stratify for 2 months at 1-5 centigrades.
Flowers in April - early May, mature fruits in late August - September. 2n=28.
Distribution.Europe (forest zone except for the northernmost and southern areas); European part of Russia (forest and forest-steppe zones); Crimea (Babugan-Yayla); Caucasus, Kazakhstan (northern, Dzungarian Alatau); Central Asia (Western Tien Shan); West and East Siberia (except for northern areas); Far East (except for Chukotka, the lower Anadyr River and Koryak Upland); Asia Minor; Mongolia; China; Korea; Japan.
Ecology.Mesophyte. Photophilous. Distributed in forest zone almost everywhere as an additive secondary tree, appears as a pioneer plant on fire sites, felled sites, wind-fallen sites, overgrowing abandoned fields etc. Forms primary forests in the West and partly in the East Siberia. Reaches the altitude of 1600 m in Altai and Eastern Sayan, up to 2000 m in Dzungarian Alatau, up to 2200 m in the Western Tien Shan, up to 2500 m on the southern slope of the Main Caucasian Range.
Utilization and economic value.Technical, medicine, ornamental. Provides valuable carpentry and building timber, fuel, stock for acetic acid, methanol, tar and wood coal. Used in officinal and folk medicine, perfume industry. Is long since widely used in planting in inhabited areas, in shelter forest stands and forestry.
References:Gubanov IA., Kiseleva KV., Novikov VS., Tikhomirov VN. 2003. Illustrated Manual of the Middle Russia Plants. V.2. Moscow: KMK. 665 p. (In Russian).
Koropachinskiy IYu., Vstovskaya TN. 2002. Woody plants of the Asian part of Russia. Novosibirsk: Publishing House of Siberian Division of the Russian Academy of Science, Branch "Geo". P.195-197. (In Russian).
Sokolov SI., Svjaseva OA., Kubli VA. 1977. Ranges of trees and shrubs of the USSR. V.1. Leningrad: Nauka. P.96-97. (In Russian).