Burke: Populus trichocarpa vs. Populus tremuloides

	Populus trichocarpa	Populus tremuloides
	black cottonwood	quaking aspen
Habit	Rough-barked, dioecious tree up to 50 m. tall; buds large, the scales very resinous, glabrous.	Colonial tree, dioecious, up to 15 m. tall, with smooth, greenish-white bark that becomes blackish and somewhat rough on very old trunks; bud scales shiny, but not resinous.
Leaves	Leaves alternate, the blades fragrant, strongly resinous, the lower side distinctly paler than the upper, variable in shape, 5-15 cm. long and 3-9 cm. wide, broadest below the middle, pointed at the tip and usually rounded or truncate at the base, the surfaces usually glabrous; petioles terete, about half as long as the blade.	Leaves alternate, relatively small, on slender, laterally-flattened petioles half to fully as long as the blade; blades rotund-ovate to reniform-cordate, 2.5-9 cm. long and 2.5-8 cm. wide, shortly acuminate, paler beneath, the margins finely toothed and hairy, the surfaces glabrous at maturity.
Flowers	Catkins drooping; the bracts subtending the flowers in the catkins lacerate-fringed; staminate catkins elongating to 2-3 cm, then deciduous; pistillate catkins at maturity 8-20 cm. long; stigmas 2, broadly dilated.	Catkins drooping; the bracts subtending the flowers in the catkins persistent, deeply cleft into a few slender lobes with long, white hairs on the margins; staminate catkins elongating to 2-3 cm. then deciduous; stamens 6-14; pistillate catkins at maturity 4-10 cm. long, with numerous fruits; stigmas 2, each deeply cleft into 2 or more slender lobes.
Fruits	Capsules rotund-ovate, 5-8 mm. long, sub-sessile.	Capsules lanceolate, 4-6 mm. long, on pedicles 1-2 mm. long

	Populus trichocarpa	Populus tremuloides
Flowering time	April-June	April-June
Habitat	Streambanks, riparian zones, river corridors, and moist woods, from sea level to middle elevations in the mountains.	Moist areas, low to fairly high elevations in the mountains
Distribution	Widely distributed on both sides of the Cascades crest in Washington; Alaska to California, east to Alberta and Wyoming. [WildflowerSearch map]	Occurring on both sides of the Cascades crest in Washington; Alaska to California, east across much of North America to the Atlantic Coast. [WildflowerSearch map] [BONAP county map]
Origin	Native	Native
Conservation status	Not of concern	Not of concern
Sibling taxa	P. alba, P. angustifolia, P. ×canescens, P. deltoides, P. nigra, P. tremuloides	P. alba, P. angustifolia, P. ×canescens, P. deltoides, P. nigra, P. trichocarpa
Web links	Local floras: CA, OR, WA Local Web sites: CalFlora, CalPhotos, 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	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, 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

Populus tremuloides

black cottonwood

quaking aspen

Habit

Rough-barked, dioecious tree up to 50 m. tall; buds large, the scales very resinous, glabrous.

Colonial tree, dioecious, up to 15 m. tall, with smooth, greenish-white bark that becomes blackish and somewhat rough on very old trunks; bud scales shiny, but not resinous.

Leaves

Leaves alternate, the blades fragrant, strongly resinous, the lower side distinctly paler than the upper, variable in shape, 5-15 cm. long and 3-9 cm. wide, broadest below the middle, pointed at the tip and usually rounded or truncate at the base, the surfaces usually glabrous;

petioles terete, about half as long as the blade.

Leaves alternate, relatively small, on slender, laterally-flattened petioles half to fully as long as the blade;

blades rotund-ovate to reniform-cordate, 2.5-9 cm. long and 2.5-8 cm. wide, shortly acuminate, paler beneath, the margins finely toothed and hairy, the surfaces glabrous at maturity.

Flowers

Catkins drooping; the bracts subtending the flowers in the catkins lacerate-fringed; staminate catkins elongating to 2-3 cm, then deciduous; pistillate catkins at maturity 8-20 cm. long;

stigmas 2, broadly dilated.

Catkins drooping; the bracts subtending the flowers in the catkins persistent, deeply cleft into a few slender lobes with long, white hairs on the margins; staminate catkins elongating to 2-3 cm. then deciduous;

stamens 6-14; pistillate catkins at maturity 4-10 cm. long, with numerous fruits;

stigmas 2, each deeply cleft into 2 or more slender lobes.

Fruits

Capsules rotund-ovate, 5-8 mm. long, sub-sessile.

Capsules lanceolate, 4-6 mm. long, on pedicles 1-2 mm. long