Burke: Alnus glutinosa vs. Alnus rubra

	Alnus glutinosa	Alnus rubra
	Black alder, European alder	Oregon alder, red alder
Habit	Multi-trunked trees to 20 meters tall.	Monoecious, deciduous trees to 25 m. tall, the bark thin, smooth and gray, the trunk up to 8 dm. thick; fresh wood tends to turn deep red.
Leaves	Blades obovate to nearly orbiculate, 3--9 × 3--8 cm, margins often irregularly doubly serrate to nearly dentate, apex often retuse or obcordate, occasionally rounded; upper and lower surfaces heavily resin-coated.	Leaves alternate, simple, the blades broadly elliptic or elliptic-ovate, 5-15 cm. long, usually acute at each end, wavy and irregularly denticulate, the margins slightly revolute, the upper surface deep green and glabrous, the lower surface rusty-gray and gland-dotted.
Flowers		Catkins developing before the leaves on growth of the previous season; staminate catkins clustered, pendulous, 5-12 cm. long; pistillate catkins cone-like, woody, ovoid-ellipsoid, 1.5-2 cm. long and 1 cm. thick, stout, thick peduncles under 1 cm. long.
Fruits		Nutlet with thin, membranous wings 1/5-1/2 as broad as the nutlet

	Alnus glutinosa	Alnus rubra
Flowering time	March-May	March-April
Habitat	Wetlands at low elevation.	Moist areas at low elevations.
Distribution	Occurring west of the Cascades crest in King County, where escaping from a wetland restoration planting. Great Lakes region east to the Atlantic Coast. [WildflowerSearch map] [BONAP county map]	Occurring chiefly west of the Cascades crest in Washington; Alaska to California, disjunct to the east in northern Idaho. [WildflowerSearch map] [BONAP county map]
Origin	Introduced from Europe	Native
Conservation status	Not of concern	Not of concern
Sibling taxa	A. incana, A. rhombifolia, A. rubra, A. viridis	A. glutinosa, A. incana, A. rhombifolia, A. viridis
Web links	Local floras: 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	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

Alnus rubra

Black alder, European alder

Oregon alder, red alder

Habit

Multi-trunked trees to 20 meters tall.

Monoecious, deciduous trees to 25 m. tall, the bark thin, smooth and gray, the trunk up to 8 dm. thick; fresh wood tends to turn deep red.

Leaves

Blades obovate to nearly orbiculate, 3--9 × 3--8 cm, margins often irregularly doubly serrate to nearly dentate, apex often retuse or obcordate, occasionally rounded; upper and lower surfaces heavily resin-coated.

Leaves alternate, simple, the blades broadly elliptic or elliptic-ovate, 5-15 cm. long, usually acute at each end, wavy and irregularly denticulate, the margins slightly revolute, the upper surface deep green and glabrous, the lower surface rusty-gray and gland-dotted.

Flowers

Catkins developing before the leaves on growth of the previous season; staminate catkins clustered, pendulous, 5-12 cm. long; pistillate catkins cone-like, woody, ovoid-ellipsoid, 1.5-2 cm. long and 1 cm. thick, stout, thick peduncles under 1 cm. long.

Fruits

Nutlet with thin, membranous wings 1/5-1/2 as broad as the nutlet

Alnus glutinosa

Alnus rubra

Flowering time

March-May

March-April

Habitat

Wetlands at low elevation.

Moist areas at low elevations.

Distribution

Occurring west of the Cascades crest in King County, where escaping from a wetland restoration planting. Great Lakes region east to the Atlantic Coast.

[WildflowerSearch map]

[BONAP county map]