Alnus incana, commonly called European gray alder, is a large pyramidal tree that grows to 40-60' tall. It is native to Europe and the Caucasus.
Subspecies rugosa, synonymous with and formerly known as Alnus rugosa, is a fast-growing, thicket forming, deciduous, spreading small tree or shrub that is native to wet sandy or gravelly soils, often along the peripheries of lakes, ponds, streams, rivers and swamps, from Hudson Bay to Newfoundland south to Minnesota, Michigan and Virginia. It is most often seen in a multi-trunked form to 15-25' tall with a broad-rounded irregular crown, but infrequently will soar to as much as 50-60' tall. It is commonly called speckled alder because of the white warty lenticils (pores) that speckle the bark. Flowers are monoecious (separate male and female flowers on the same tree), appearing in catkins in March-early April before the leaves emerge. Male catkins (flowers purplish-brown with yellow pollen) are slender, cylindrical and droop to 1 1/2" long. Female catkins (flowers green) are rounded (to 1/2") and clustered on stalks. Female catkins are followed by 1-inch long fruiting cones (strobiles) composed of winged seeds. These fruiting cones mature to reddish-brown in fall with persistence into winter, resemble small pine cones and are attractive to birds. Female flowers are pollinated by wind. Leathery dull green leaves (2-4" long) with wrinkled surfaces and red-hairy undersides are wedge-shaped at the base and pointed at the tip with doubly serrate margins. Insignificant fall color. Root nodules fix nitrogen. Alnus incana subsp. rugosa is very similar in appearance to Alnus serrulata (smooth alder or hazel alder). Rugosa means wrinkled in reference to sunken veins on lower leaf surfaces.
Genus name is the Latin name for alder.
Specific epithet means gray or hoary in reference to leaf color.