OregonFlora: Betula pumila

	Betula pumila
	bog birch
Habit	Shrubs to 6 m; bark dark brown with pale lenticels, dull, not exfoliating.
Twigs	ascending, finely puberulent with hairs to 0.1 mm and spreading hairs ~0.3–0.4 mm; when young dry or glutinous, with scattered resin-blisters.
Leaves	blades obovate, elliptic, or almost circular, 22–40 × 15–31 mm, green above, light green beneath; firm but flexible, bases obtuse or rounded; margins crenate from base to tip with 14–19 strong rounded crenations on each margin, usually all approximately same size, 1–2 mm; secondary veins obscure, 4–6 on each side; tips broadly obtuse or rounded; surfaces glabrous; petioles 4–7 mm, glabrous or puberulent.
Fruits	very narrowly winged.
Pistillate catkins	15–23 mm; bracts with lateral lobes often shorter and broader than middle lobe.

	Betula pumila
Distribution	[WildflowerSearch map] [BONAP county map]
Discussion	Boggy margins of lakes. Flowering May–Jun. 0–1300 m. Casc, ECas, WV. CA, ID, WA; north to Yukon, east to Newfoundland. Native. Many specimens of B. pumila from eastern North America have longer, denser pubescence on the twigs and few or no glandular blisters. Our western plants, with sparser pubescence and more numerous glands, are sometimes separated as a distinct taxon (B. hallii or B. pumila var. glandulifera; Dugle 1966; Hitchcock & Cronquist 1964), but the two forms intergrade. Furlow (1997) argues against recognizing segregate taxa.
Source	Flora of Oregon, volume 2, page 383 Alan Whittemore
Sibling taxa	B. glandulosa, B. occidentalis, B. papyrifera, B. pendula
Synonyms	Betula glandulosa var. hallii, Betula pumila var. glandulifera
Web links	Local floras: BC, OR, WA Local Web sites: Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search

Betula pumila

bog birch

Habit

Shrubs to 6 m; bark dark brown with pale lenticels, dull, not exfoliating.

Twigs

ascending, finely puberulent with hairs to 0.1 mm and spreading hairs ~0.3–0.4 mm; when young dry or glutinous, with scattered resin-blisters.

Leaves

blades obovate, elliptic, or almost circular, 22–40 × 15–31 mm, green above, light green beneath; firm but flexible, bases obtuse or rounded;

margins crenate from base to tip with 14–19 strong rounded crenations on each margin, usually all approximately same size, 1–2 mm;

secondary veins obscure, 4–6 on each side;

tips broadly obtuse or rounded;

surfaces glabrous;

petioles 4–7 mm, glabrous or puberulent.

Fruits

very narrowly winged.

Pistillate catkins

15–23 mm;

bracts with lateral lobes often shorter and broader than middle lobe.

Betula pumila

Distribution

[WildflowerSearch map]

[BONAP county map]

Discussion

Boggy margins of lakes. Flowering May–Jun. 0–1300 m. Casc, ECas, WV. CA, ID, WA; north to Yukon, east to Newfoundland. Native.

Many specimens of B. pumila from eastern North America have longer, denser pubescence on the twigs and few or no glandular blisters. Our western plants, with sparser pubescence and more numerous glands, are sometimes separated as a distinct taxon (B. hallii or B. pumila var. glandulifera; Dugle 1966; Hitchcock & Cronquist 1964), but the two forms intergrade. Furlow (1997) argues against recognizing segregate taxa.

Source

Flora of Oregon, volume 2, page 383
Alan Whittemore

Sibling taxa

B. glandulosa, B. occidentalis, B. papyrifera, B. pendula

Synonyms

Betula glandulosa var. hallii, Betula pumila var. glandulifera

Web links