Betula pumila
Betula nigra
bog birch, bouleau nain, dwarf birch, glandular birch, low birch, scrub birch, swamp birch
red birch, river birch
of mature trunks and branches grayish brown, yellowish, reddish, or creamy white, smooth, irregularly shredding and exfoliating in shaggy sheets when mature;
lenticels dark, horizontally expanded.
without taste and odor of wintergreen, glabrous to moderately pubescent, with scattered small resinous glands, especially near nodes.
without wintergreen taste or odor, glabrous to sparsely pubescent, often with scattered, tiny, 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 rhombic-ovate, with 5–12 pairs of lateral veins, 4–8 × 3–6 cm, base broadly cuneate to truncate, margins coarsely doubly serrate to dentate, apex acuminate;
surfaces abaxially moderately pubescent to velutinous, especially along major veins and in vein axils, often with scattered, 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, conic or nearly globose, 1.5–3 × 1–2.5 cm, shattering with fruits in late spring or early summer;
scales often persistent into early winter, lobes 3, ascending, branching distal to middle, narrow, elongate, equal to somewhat unequal in length, apex acute.
with wings slightly narrower than body, broadest near center, not extended beyond body apically.
with wings narrower than body, usually broadest near summit, not extended beyond body apically.
= 56.
= 28.
Betula pumila
Betula nigra
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 nigra is a large and characteristic floodplain tree. Like several other species of this habitat (e.g., Acer saccharinum Marshall and Ulmus americana Linnaeus), it releases its fruits in early summer; the seeds germinate immediately (at a time when the surrounding land is unlikely to be flooded). The wood of Betula nigra is not in high demand for timber because of its generally poor quality. Cultivars with freely exfoliating bark are commonly cultivated in the Northeast and Midwest.
Native Americans used Betula nigra medicinally to treat dysentery, colds, and milky urine (D. E. Moerman 1986).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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