Burke: Alnus glutinosa vs. Alnus rhombifolia

	Alnus glutinosa	Alnus rhombifolia
	Black alder, European alder	California alder, white alder
Habit	Multi-trunked trees to 20 meters tall.	Monoecious, deciduous small trees 5-20 m. tall, the old bark light-colored, the new growth puberulent.
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 elliptic or oblong-rhombic, 4-8 cm. long, acute to rounded at each end, finely to coarsely once- or twice-serrate, not wavy, hairy at least beneath, the upper surface deeper green.
Flowers		: Catkins developing before the leaves on growth of the previous season; staminate catkins slender, pendulous, 4-8 cm. long, the stamens usually 2 per flower; pistillate catkins cone-like, woody, 10-15 mm. long, on stout peduncles often as long as the catkin.
Fruits		Nutlet thin-margined but without a true wing.

	Alnus glutinosa	Alnus rhombifolia
Flowering time	March-May	January-April
Habitat	Wetlands at low elevation.	Near streams 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 east of the Cascades crest in Washington; Washington to California and Nevada, east to 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. rubra, 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: 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 rhombifolia

Black alder, European alder

California alder, white alder

Habit

Multi-trunked trees to 20 meters tall.

Monoecious, deciduous small trees 5-20 m. tall, the old bark light-colored, the new growth puberulent.

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 elliptic or oblong-rhombic, 4-8 cm. long, acute to rounded at each end, finely to coarsely once- or twice-serrate, not wavy, hairy at least beneath, the upper surface deeper green.

Flowers

: Catkins developing before the leaves on growth of the previous season; staminate catkins slender, pendulous, 4-8 cm. long, the stamens usually 2 per flower; pistillate catkins cone-like, woody, 10-15 mm. long, on stout peduncles often as long as the catkin.

Fruits

Nutlet thin-margined but without a true wing.

Alnus glutinosa

Alnus rhombifolia

Flowering time

March-May

January-April

Habitat

Wetlands at low elevation.

Near streams 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]