Alnus viridis (Green Alder)

Plant Info
Also known as: Mountain Alder
Family:Betulaceae (Birch)
Life cycle:perennial woody
Habitat:part shade, sun; average moisture; mixed forest, clearings, river banks, shores, rock outcrops, bluffs, cliffs
Bloom season:May - June
Plant height:6 to 14 feet
Wetland Indicator Status:GP: FAC MW: FAC NCNE: FAC
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: indistinct Cluster type: raceme Cluster type: spike

[photo of flowers] Male and female flowers are borne separately on the same plant (monoecious), in clusters called catkins, blooming in spring when leaves emerge. Two to 4 male catkins are clustered at the tip of 1 year old twigs, pendent in flower, 1¼ to 3½ inches long. At anthesis, female catkins are erect, red, narrowly cylindric, up to about 1/3 inch long, in one or more separate clusters near the male catkins on the same branch, with 2 to 10 catkins in a cluster. Catkins develop in late summer, the males as slender spikes of tightly appressed scales and females more bud-like, persist through winter and open up the following spring.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of leaves] Leaves are alternate and simple, 2 to 3½ inches long, 1 to 2½ inches wide, egg-shaped to elliptic, pointed to rounded at the tip, the base rounded to somewhat heart-shaped, on a hairy stalk up to about ¾ inch long. Edges are finely toothed and not double-toothed. The upper surface is dark green, hairless to sparsely hairy, the lower surface shiny green and hairless to sparsely hairy, especially along the veins, and typically sticky when young. Twigs are brown to reddish brown to grayish, with scattered white lenticels (pores), new growth hairless to sparsely hairy and becoming hairless and smooth the second year. Buds are erect, elliptic, have 4 to 6 scales and are stalkless or nearly so.

[photo of trunk] Older bark is grayish to reddish brown, smooth with scattered pale horizontal lenticels. Stems are multiple from the base, the larger trunks up to 1¾ inches diameter.

Fruit: Fruit type: seed without plume

[photo of mature fruit] Female catkins become stout, oval to egg-shaped, cone-like clusters up to about ¾ inch long, containing broadly-winged nutlets each 1/8 inch long, green drying to brown.


Green Alder is a shrub of our northern forests and the rocky north shore of Lake Superior. It is very similar to the related Speckled Alder (Alnus incana), which has buds that are more distinctly stalked, narrowly-winged nutlets, leaves that are not shiny on the underside, typically more coarsely double-toothed with shallowly-lobed edges, female catkins are shorter, stalkless and not erect, and flowers open before leaves emerge in spring. While Green Alder can spread from root suckers, it spreads slowly and rarely forms dense thickets like Speckled Alder does. There are at least 4 recognized subspecies of Aluns viridis: subsp. viridis limited to Europe, subsp. sinuata and fruticosa present in the northwest US into Canada and Alaska with double-toothed leaves, and subsp. crispa with finely serrated leaves present throughout most of Canada and into New England and the northern Great Lakes region, including Minnesota.

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More photos

Photos by K. Chayka taken in Cook County. Photos courtesy Peter M. Dziuk taken in Cook and Lake counties.


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Susan Premo - Buyck Minnesota
on: 2023-08-14 13:19:31

Seems there's green alder wherever the loggers go. And other areas too, ofcourse.

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