Alnus incana (Speckled Alder)
|Also known as:
|sun; wet; bogs, swamps, shores, stream banks, swales, borders of wet meadows
|March - May
|10 to 25 feet
|Wetland Indicator Status:
|GP: FACW MW: FACW NCNE: FACW
|MN county distribution (click map to enlarge):
|National distribution (click map to enlarge):
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Male and female flowers are borne separately on the same plant (monoecious), in clusters called catkins, blooming in very early spring before leaves emerge. Two to 6 male catkins are clustered at the tip of 1 year old twigs, pendent in flower, 1¾ to 3½ inches long. Female catkins are red, oval to short-cylindric, about ¼ inch long at anthesis, in one or more separate clusters near the male catkins on the same branch, with 1 to 4 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:
Leaves are alternate and simple, 1½ to 4½ inches long, 1 to 3 inches wide, egg-shaped to elliptic, pointed or blunt at the tip, the base rounded to wedge-shaped, on a hairy stalk up to about ¾ inch long. Edges are coarsely double-toothed and usually have a few to several shallow lobes. The upper surface is dark green, hairless to sparsely hairy, the lower surface dull green and hairy, especially along the veins.
Twigs are brown to reddish brown to grayish, with scattered white lenticels (pores), new growth is hairy but becoming hairless and smooth the second year. Buds are erect, elliptic, have 2 or 3 scales and a short but obvious stout stalk.
Older bark is grayish to reddish brown with pale horizontal lenticels (pores). Stems are usually numerous from the base, the larger trunks up to 6 inches diameter, occasionally taking the form of a small tree.
Speckled Alder is a common, large, multi-stemmed wetland shrub, often forming dense thickets from root suckering as well as a process called “layering”, where low branches take root then detach from the mother plant and grow independently. You can find some very cool plants growing in Alder thickets, but there is no worse habitat to trudge around in—only a buckthorn-infested woods might be worse! It is very similar to the related Green Alder (Alnus viridis), which has buds that are stalkless or nearly so with 4 to 6 scales, broadly-winged nutlets, leaves that are typically more finely toothed, shiny on the lower surface and do not have shallowly-lobed edges, female catkins are erect and more elongated on elongating stalks, flowers open when leaves emerge in spring, and is generally a smaller shrub often found in more upland habitats. There are 2 recognized subspecies of Alnus incana in North America: subsp. tenuifolia is a western species with thin, papery leaves and rounded teeth, and subsp. rugosa with thicker leaves and sharply pointed teeth, present in eastern North America including Minnesota.
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- Speckled Alder shrub
- a thicket of Speckled Alder
- Alder thicket at the end of September
- Speckled Alder in winter
- older bark can be quite warty
- stems are numerous from the base
- more leaves
- leaf hairs and vein pattern
- this year's developing fruit
- next year's catkins developing in late summer
- next year's catkins developing with this year's fruit
Photos courtesy Peter M. Dziuk taken in Anoka and Hubbard counties and in Wisconsin.
Have you seen this plant in Minnesota, or have any other comments about it?