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Betula
Family: Betulaceae
Betula image
Al Schneider
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John J. Furlow in Flora of North America (vol. 3)
Trees or shrubs , to 30 m; trunks often several, branching excurrent, becoming deliquescent. Bark of trunks and branches dark brown to chalky white, smooth, often exfoliating; lenticels dark, prominent, sometimes horizontally expanded. Wood nearly white to reddish brown, light and soft to moderately heavy and hard, texture fine. Branches, branchlets, and twigs nearly 2-ranked; young twigs differentiated into long and short shoots, sometimes with taste and odor of wintergreen. Winter buds sessile, slender, terete, apex acute; scales several, imbricate, smooth. Leaves mostly on short shoots, nearly 2-ranked. Leaf blade ovate to deltate, elliptic, or nearly orbiculate, 0.5--10(--14) × 0.5--8 cm, thin, margins doubly serrate or serrate (or crenate to shallowly round-lobed in dwarf northern species); surfaces glabrous to tomentose, sometimes abaxially resinous-glandular. Inflorescences: staminate catkins mostly terminal on branchlets, solitary or in small racemose clusters, formed previous growing season and often exposed during winter, expanding with leaves; pistillate catkins proximal to staminate catkins, mostly solitary, erect, ovoid to cylindric, firm; scales and flowers crowded, enclosed within buds during winter, expanding with leaves. Staminate flowers in catkins 3 per scale; stamens (1--)2--3(--4), filaments divided below anthers, nearly to base. Pistillate flowers (1--)3 per scale. Infructescences erect or pendulous; scales usually deciduous with release of fruits (although persisting into winter in a few species), (1--)3-lobed, thickened or leathery but not woody. Fruits samaras, lateral wings 2, moderately wide to broad, membranaceous. x = 14. Birches, like alders, are common trees and shrubs of northern temperate and boreal zones of the Northern Hemisphere. Like Alnus , the group is highly diversified, especially in the Old World. The species are well known for their free hybridization, and specimens are therefore frequently difficult to identify. Birches occupy habitats in cool, moist regions, including peatlands, stream banks, and lakeshores, cool, damp woods, and moist slopes in cool coves. The wood of species that grow to a large size (including especially B . alleghaniensis ) has many uses, including the manufacture of doors and windows, flooring, cabinetry, interior molding, wood paneling, furniture, and plywood. Betula sect. Costatae (Regel) Koehne consists of large, mesophytic trees, often with dark, close or exfoliating bark, large thin leaves, infructescence scales with long narrow lobes, and fruits with narrow wings. North American representatives of this group include Betula alleghaniensis , B . lenta , and B . nigra . The mostly circumboreal Betula sect. Betula consists of small to medium trees with rather large thin leaves and fruits with wide wings (wider than the fruit body). A characteristic feature of trees in this group is their white bark that often peels apart in sheets. These include the familiar paper birch, B . papyrifera , and its European counterpart, B . pubescens , as well as the common eastern B . neoalaskana . A third line, Betula sect. Humiles W. D. Koch, consists of dwarf shrubby species of the cold circumpolar region. In North America this section is represented by B . glandulosa , B . pumila , and B . nana .

Birches are a difficult group taxonomically because of their high vegetative variability and frequent hybridization. Many morphologic and cytologic studies have attempted to deal with variation within the genus or its subgroups. Species of Betula form a polyploid series, with chromosome numbers of 2 n = 28, 56, 70, 84, and 112, plus additional numbers in some hybrids. This and other research in the genus has been reviewed by J. J. Furlow (1990).

JANAS 33(1)
PLANT: Trees or shrubs to 30 m tall; trunks often several; twigs nearly 2-ranked, differentiated into long and short shoots; winter buds sessile, with several imbricate scales; bark of trunks and branches dark brown or reddish to white, often exfoliating; lenticels conspicuous. INFLORESCENCE: staminate catkins solitary or in racemose clusters, formed the previous growing season, expanding with the leaves; pistillate catkins mostly solitary, proximal to staminate catkins, erect or sometimes becoming pendulous in fruit, the scales and flowers crowded and enclosed within the buds during winter, deciduous in fruit. LEAVES: mostly on short shoots, nearly 2-ranked; blades ovate to deltoid, elliptic, or nearly orbiculate; margins serrate, doubly serrate, or crenate; surfaces glabrous to tomentose, sometimes abaxially resinous. STAMINATE FLOWERS: 3 per scale; stamens (1-)2-3(-4), the filaments divided below the anthers, the 2 anther sacs separate. PISTILLATE FLOWERS: 1-3 per scale. FRUITS: tiny leathery samaras; wings 2, lateral, membranaceous. x = 14. NOTES: Ca. 50 spp.; circumboreal. (Latin betula = birch). Species of Betula yield important wildlife food, wood for interior finishing, and popular ornamentals. NOTES: Brasher, Jeffrey W. 2001. Betulaceae. J. Ariz. - Nev. Acad. Sci. Volume 33(1)
Vascular plants of NE US and adjacent Canada
Staminate catkins elongate, the scales ovate to rotund, each subtending 3 fls; cal minute, 4-parted or usually 2-parted, one lobe much exceeding the other; stamens 2, each short filament divided near the summit and the anther-sacs separate; pistillate catkins ovoid to cylindric, the scales closely imbricate, generally 3-lobed, relatively thin, at maturity herbaceous or coriaceous, deciduous with or soon after the frs, the catkin disintegrating; fr ordinarily a small samara, the elliptic body with 2 membranous lateral wings and terminated by the short, persistent styles, or sometimes the wings virtually obsolete; trees or shrubs, the bark often separable into thin layers; the catkins appear in the fall and come into anthesis early in the spring (midsummer in B. michauxii). 50, N. Hemisphere. The taxonomy of Betula is complicated by extensive hybridization and introgression, yet the species maintain their identity over large areas of sympatry. Many of the hybrids have been given names. B. آorealis Spach is B. papyrifera נpumila; B. أaerulea Blanch. and B.أaerulea-grandis Blanch. are B. papyrifera var. cordifolia נpopulifolia; B. حinor (Tuck.) Fernald is B. glandulosa var. glandulosa נa dwarf, alpine form of B. papyrifera, perhaps locally alloploid; B. ذurpusii C. K. Schneid. is B. alleghaniensis נpumila; B. حurrayana B. V. Barnes & Dancik is an octoploid back-cross of B. ذurpusii with B. alleghaniensis; and B. سandbergii Britton is B. glandulosa var. glandulifera נpapyrifera.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

©The New York Botanical Garden. All rights reserved. Used by permission.
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Betula alajica
Image of Betula alajica
Betula alaskana
Image of Betula alaskana
Betula alba
Image of Betula alba
Betula albosinensis
Image of Betula albosinensis
Betula alleghaniensis
Image of Betula alleghaniensis
Betula alnoides
Image of Betula alnoides
Betula alnus
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not available
Betula andrewsii
Image of Betula andrewsii
Betula borealis
Image of Betula borealis
Betula caerulea
Image of Betula caerulea
Betula chinensis
Image of Betula chinensis
Betula cordifolia
Image of Betula cordifolia
Betula corylifolia
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Betula costata
Image of Betula costata
Betula divaricata
Image of Betula divaricata
Betula dugleana
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Betula dutillyi
Image of Betula dutillyi
Betula eastwoodiae
Image of Betula eastwoodiae
Betula ermanii
Image of Betula ermanii
Betula exilis
Image of Betula exilis
Betula fargesii
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Betula forrestii
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Betula fruticosa
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Betula glandulifera
Image of Betula glandulifera
Betula glandulosa
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Betula grossa
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Betula hornei
Image of Betula hornei
Betula humilis
Image of Betula humilis
Betula jackii
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Betula jacquemontii
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Betula japonica
Image of Betula japonica
Betula jarmolenkoana
Image of Betula jarmolenkoana
Betula kamtschatica
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Betula kenaica
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Betula kirghisorum
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Betula kweichowensis
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Betula lanata
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Betula lenta
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Betula litwinowii
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Betula luminifera
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Betula lutea
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Betula mandshurica
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Betula maximowicziana
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Betula medwediewii
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Betula michauxii
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Betula microphylla
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Betula minor
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Betula murrayana
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Betula nana
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Betula neoalaskana
Image of Betula neoalaskana
The National Science Foundation
Development supported by National Science Foundation Grants (DBI 9983132, BRC 0237418, DBI 0743827, DBI 0847966)
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