Betula pumila
Betula populifolia
bog birch, bouleau nain, dwarf birch, glandular birch, low birch, scrub birch, swamp birch
bouleau gris, bouleau à feuilles de peuplier, fire birch, gray birch, white birch
when young dark reddish brown, in maturity becoming grayish white, smooth, close;
lenticels dark, horizontally expanded.
without taste and odor of wintergreen, glabrous to moderately pubescent, with scattered small resinous glands, especially near nodes.
without taste and odor of wintergreen, glabrous to sparsely pubescent, dotted with small, inconspicuous, resinous glands.
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 broadly ovate to deltate or rhombic with 5–18 pairs of lateral veins, 3–10 × 3–8 cm, base truncate to cuneate, marginally coarsely, irregularly, or sometimes obscurely doubly serrate, apex abruptly long-acuminate;
surfaces abaxially glabrous or sparsely pubescent, often covered with minute, resinous glands.
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.
erect to nearly pendulous, nearly cylindric, 1–2.5(–3) × 0.8–1 cm, shattering with fruits in early fall;
scales adaxially densely pubescent, lobes diverging distal to middle, central lobe cuneate, acute, much shorter than lateral lobes, lateral lobes divergent, broad, irregularly angular.
with wings slightly narrower than body, broadest near center, not extended beyond body apically.
with wings much broader than body, broadest near middle, often extended beyond body both apically and basally.
= 56.
= 28.
Betula pumila
Betula populifolia
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.)
Betula populifolia is an important successional tree on burned, cleared, or abandoned land in the Northeast. It is closely related to Betula pendula Roth of Europe, B. neoalaskana of the Northwest, and several Asian taxa. This species is easily distinguished from the paper birch, with which it is often sympatric, by the long tapering apices of its leaves, its nonpeeling bark, and the characteristic expanded, black triangular patches on the trunks below the branches.
The Iroquois used Betula populifolia medicinally to treat bleeding piles, and the Micmac, to treat infected cuts and as an emetic (D. E. Moerman 1986).
The blue birches (Betula ×caerulea Blanchard) have been variously considered to repres species or a hybrid between B. papyrifera Marshall and B. populifolia Marshall (T. C. Brayshaw 1966) or B. papyrifera and the big blue birch B. caerulea-grandis (M. L. Fernald 1922). Both B. ×caerulea and B. caerulea-grandis have been shown in more recent experimental studies to be of hybrid origin between B. cordifolia Regel and B. populifolia (A. G. Guerriero et al. 1970; W. F. Grant and B. K. Thompson 1975; P. E. DeHond and C. S. Campbell 1989). Individuals of these hybrids combine characteristics of the parents, the infructescence scales and leaves somewhat resembling those of B. populifolia, and the habit and exfoliating reddish bark that of B. cordifolia.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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