Betula pumila |
Betulaceae |
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bog birch, bouleau nain, dwarf birch, glandular birch, low birch, scrub birch, swamp birch |
birch family |
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Habit | Shrubs, coarse, irregular, or spreading, to 4 m. Bark dark reddish brown, smooth, close; lenticels pale, inconspicuous. | Trees and shrubs, deciduous. | ||||||||||||||||
Twigs | without taste and odor of wintergreen, glabrous to moderately pubescent, with scattered small resinous glands, especially near nodes. |
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Leaves | blade elliptic, obovate, or nearly orbiculate (to sometimes reniform) with 2–6 pairs of lateral veins, 2.5–5(–7) × 1–5 cm, base cuneate to rounded, margins crenate to dentate, apex usually broadly acute or obtuse to rounded; surfaces abaxially glabrous or slightly pubescent to heavily velutinous or tomentose, often with scattered resinous glands. |
blade sometimes lobed, pinnately veined, margins toothed, serrate to nearly entire; surfaces glabrous to tomentose, abaxially often with resinous glands. |
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Inflorescences | unisexual; staminate catkins pendulous, elongate, cylindric, conspicuously bracteate, consisting of crowded, reduced, 1–3-flowered clusters; pistillate inflorescences either of erect to pendulous bracteate catkins, or of compact 2–3-flowered clusters subtended by leafy involucres; bracts often nearly foliaceous or woody in infructescences. |
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Staminate flowers | bracteate; stamens (1–)4–6; anthers 2-locular, dehiscing by longitudinal slits, pollen sacs often ± distinct; pistillode sometimes present. |
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Pistillate flowers | small, highly reduced; pistil 1, 2(–3)-carpellate; ovary inferior, usually 2-locular proximally, 1-locular distally; placentation axile; ovules 1–2 per locule, pendulous; styles 2, distinct or nearly so; stigmas dry; staminodes usually absent. |
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Infructescences | erect, cylindric, 0.8–1.5(–2) × 0.8–1 cm, shattering with fruits in fall; scales glabrous to pubescent, lobes diverging slightly distal to middle, central lobe narrow, elongate, lateral lobes shorter and broader, extended. |
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Fruits | nuts, nutlets, or 2-winged samaras, 1-seeded, without multibracteate cupule, often subtended or enclosed by foliaceous hull developed from 2–3 bracts; seed coat membranous; endosperm present, thin at maturity; embryo straight, as long as seed; cotyledons flat or greatly thickened, oily. |
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Samaras | with wings slightly narrower than body, broadest near center, not extended beyond body apically. |
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Winter | buds stipitate or sessile, with either 2–3 valvate scales (stipules) or few to many imbricate scales (or occasionally naked); terminal bud absent. |
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2n | = 56. |
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Betula pumila |
Betulaceae |
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Phenology | Flowering late spring. | |||||||||||||||||
Habitat | Bogs, calcareous fens, wooded swamps, muskegs, lake shores | |||||||||||||||||
Elevation | 0–700 m (0–2300 ft) | |||||||||||||||||
Distribution |
CA; CO; CT; IA; ID; IL; IN; KS; MA; ME; MI; MN; MT; ND; NE; NJ; NY; OH; OR; PA; SD; VT; WA; WI; WY; AB; BC; MB; NB; NF; NS; NT; ON; PE; QC; SK; YT; SPM
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Primarily boreal and cool temperate zones of Northern Hemisphere |
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Discussion | Betula pumila is sometimes treated (in part) as a variety of B. glandulosa Michaux, to which it is related at a subgeneric or sectional level. On the basis of morphology, however, it forms a cohesive and distinct entity (J. J. Furlow 1984). The two main varieties into which B. pumila is often divided (a more southern B. pumila var. pumila, with mostly pubescent, glandless leaves, and a more northern B. pumila var. glandulifera, with less pubescent, gland-bearing leaves) may represent geographic races; these are not well marked, however, and they do not hold up well when the complex is examined as a whole. The Ojibwa used Betula pumila medicinally as a gynecological aid and as a respiratory aid (D. E. Moerman 1986). (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Genera 6, species ca. 125 (5 genera, 33 species in the flora). Betulaceae belong to an ancient lineage, traceable in the fossil record to the upper Cretaceous. They are easily distinguished by their woody habit; simple, pinnately veined, usually ovate, sharp-toothed leaves; long staminate catkins that often develop the season before anthesis; and (except in Corylus and Ostryopsis) strobiluslike infructescences. The family is held together on the basis of many features, including habit, leaf structure and arrangement, trichome morphology, wood anatomy, inflorescence morphology, ovary and ovule structure, pollen morphology, embryo structure, and fertilization and germination patterns. Five of the six constituent genera inhabit the boreal and cool temperate zones of Eurasia, North America, and the mountains of Mexico and Central America, and two genera also grow in the Andes to northern Argentina in South America. The remaining genus, Ostryopsis Decaisne (most closely related to Corylus Linnaeus), consists of two species of shrubs restricted to northern and western China. The group is sometimes divided into two families, Betulaceae (Alnus and Betula) and Corylaceae (Carpinus, Ostrya, Corylus, and Ostryopsis), especially in Europe (e.g., H. K. Airy Shaw in J. C. Willis 1973; R. M. T. Dahlgren 1980; J. Hutchinson 1959). In America, this treatment has been followed by A. J. Rehder (1940), J. K. Small (1903), and a few others. Some of those writers have based their recognition of two families in part on the belief that a fundamental difference exists in the staminate inflorescences of the two groups. This view is no longer widely accepted, and most modern authors maintain the family as a single group composed of two subfamilies, Betuloideae and Coryloideae. Betulaceae may have been derived from hamamelidaceous stock (O. Tippo 1938); this idea has been advanced by others (e.g., J. A. Doyle 1969; P. K. Endress 1977; M. W. Chase et al. 1993). The ancestor of more advanced Hamamelidae (including Betulaceae) may have been a member of the Normapolles complex, a Cretaceous fossil pollen flora that includes grains similar in structure to those of the modern Betulaceae (J. A. Doyle 1969). The pollen of modern Betulaceae is much more specialized than that of modern Hamamelidales, however, and the relationships of the Normapolles complex to Juglandaceae, Fagaceae, and other amentiferous groups, as well as to Betulaceae, are not certain. Additional fossil information will be needed if botanists are to gain stronger insights into the phylogeny of these families (P. R. Crane 1989; K. C. Nixon 1989). The most obvious evolutionary trends within the family are those related to fruit dispersal (winged fruits in the Betuloideae, nutlets with accessory winglike bracts in Carpinus and Ostrya, and dispersal by small mammals in Corylus), and with apparent adaptations for survival in cold climates (including shrubby growth forms, small leaves, and the protection of pistillate catkins during winter by bud scales in boreal species). Some radiation has also occurred with respect to the pollination system (E. J. Jäger 1980). Please see P. R. Crane (1989) and J. J. Furlow (1990) for reviews of literature related to the origin and diversification of the family. Members of Betulaceae are economically important as timber trees, as the source of hazelnuts and filberts (Corylus), as ornamental trees and shrubs, and as aids in soil nitrification and stabilization (Alnus). Some are important as causes of pollen allergies in regions where they grow abundantly. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 3. | FNA vol. 3, p. 507. | ||||||||||||||||
Parent taxa | Betulaceae > subfam. Betuloideae > Betula | |||||||||||||||||
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Subordinate taxa | ||||||||||||||||||
Synonyms | B. borealis, B. glandulifera, B. glandulosa var. glandulifera, B. glandulosa var. hallii, B. hallii, B. nana var. glandulifera, B. pubescens subsp. borealis, B. pumila var. glabra, B. pumila var. glandulifera, B. pumila var. renifolia | |||||||||||||||||
Name authority | Linnaeus: Mant. Pl., 124. (1767) | Gray | ||||||||||||||||
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