Alnus viridis ssp. crispa

Green Alder

Green Alder with cones
Photo © by Earl J.S. Rook

Flora, fauna, earth, and sky...
The natural history of the northwoods


  • Alnus, from the Latin for the alder
  • viridis, from the Latin, "green"
  • crispa, from the Latin, "curly"
  • Other common names include American Green Alder, Mountain Alder, Tag Alder, Aulne Vert, Aulne Crisp (Qué)


  • Kingdom Plantae, the Plants
    • Division Magnoliophyta, the Angiosperms (flowering plants)
      • Class Magnoliopsida, the Dicotyledons
      • Subclass Hamamelididae
        • Order Fagales
          • Family Betulaceae, the Birches
            • Genus Alnus, the Alders
  • Taxonomic Serial Number: 181894
  • Also known as Alnus alnobetula, Alnus ovata, Alnus crispa, Alnus crispa var. elongata, Alnus crispa var. mollis, Alnus crispa fruticosa, Alnus X hultenii, Duschekia viridis, Alnus viridis var. crispa, Alnus viridis ssp. fruticosa.


  • A tall, deciduous, thicket-forming, rhizomatous shrub or small tree, to 10' tall, occasionally 20'-30'.
  • Leaves ovate or elliptic; glabrous above, but pubsecent below, lightly to heavily resin-coated. Margins serrated with very fine teeth. Do not turn color, but remain green until dropped in the fall.
  • Stem
    • Twigs have sessile, pointed axillary buds.
    • Bark smooth, yellowish-brown, with small, scattered pale lenticels..
  • Roots shallow, with nodules containing nitrogen-fixing microorganisms.
  • Flowers: Male catkins and female flowers on same plant.
    • Staminate catkins in single cluster of 2-4, formed late in growing season before flowering and exposed during winter
    • Pistillate catkins in 1 or more clusters of 2-10, formed season before blooming, enclosed in buds during winter, exposed with new growth in spring.
  • Fruit a small, dry woody cone on long, thin stems.
  • Seed a samara, elliptic to obovate, with wings wider than body.


  • Identifiable as an Alder/Hazel by its coarse, toothed leaves and shrubby growth form
  • Distinguished from other Alder/Hazel with some difficulty
  • Field Marks
    • Sessile winter buds


  • Northwest Territories to Labrador, Newfoundland, and Greenland; south to the Prairie Provinces, NE Minnesota, Northern Wisconsin, the UP, Northern New York, Vermont, New Hampshire, Maine, and the Maritimes. Isolated populations in the Appalachians.


  • From open tundra to open conifer forest but cannot withstand a dense overstory. Singly or in thickets along streams, lakeshores, coasts, bogs, or muskeg margins, and as an understory component in conifer forests. Usually associated with some source of moisture, but is adapted to somewhat drier conditions than other alders. Wetter sites are more favorable for high nitrogen-fixing activity.
  • Soil textures range from sandy to gravelly or rocky; often occurs on morainal soil left by retreating glaciers. Soils in deglaciated areas are generally acidic (pH 5.0-6.5).
  • Semi-shade tolerant and considered a pioneer species. After fire, sprouts from the root crown and establishes by seed from plants in adjacent unburned areas. The bare mineral soils created by these disturbances are prime sites. These shrubs provide shade that reduces soil temperatures, allowing spruce and other genera to establish.
  • A dominant or codominant in a variety of habitats, it may occur as an understory dominant in open conifer forests with Black Spruce (Picea mariana), White Spruce (Picea glauca), and Jack Pine (Pinus banksiana) overstories; and in open and closed deciduous forests with Paper Birch (Betula papyrifera), Quaking Aspen (Populus tremuloides), Balsam Poplar (Populus balsamifera), overstories.
  • Can be a major competitor of conifer seedlings. Dense thickets can prevent conifer establishment over large areas. However, due to its nitrogen-fixing ability, alder can improve soil fertility. It is also a nurse tree for conifers such as spruce (Picea spp.) and pine (Pinus spp.) on nitrogen-deficient soils.


  • Survives fire through persistent root crowns. Sprouting occurs from underground stems at or within 2" of the soil surface.
  • Fire kills the aboveground portion of the plant. Root crowns in the mineral soil burn only under the most severe conditions, but they can be killed by the heat generated during a fire. Severe fires that remove the organic layer and expose and char root crowns can completely eliminate sprouting.
  • Open-growing alders more vulnerable to fire than thicket-growing alders because very little understory fuel accumulates in alder thickets.
  • Considered a survivor species, sprouting from basal or underground parts following fire. Additionally, its wind-dispersed seeds quickly colonize bare mineral soils exposed by fire. Regeneration from sprouting and the establishment of seedlings allow reestablishment at a fairly rapid rate following fire. Very adaptable and successful regardless of length of the fire cycle. Does not burn easily, and dense stands can sometimes prevent fire spread. The sprouting response is usually immediate and generally results in an increased number of plants. American green alder also reestablishes by seed dispersed from adjacent, unburned areas. Abundant in areas with a history of frequent fires. This nitrogen-fixing alder may be favored over other invading species by severe fires that remove the surface organic matter. Alder invasion and persistence are favored by fire, but total recovery is slow. Repeated fires in wet sites can result in thickets of alder.




  • Bark is very astringent and has been used medicinally by Native Americans.
  • It has also been used in the tanning of leather and dying of textiles.


  • Reproduces by seed and vegetatively by rhizomes. Germination from seed on disturbed habitats is the primary form of reproduction. The seeds invade and colonize bare mineral soil.
  • Sexual reproduction: Monoecious. Wind pollinated. The female catkins turn woody and conelike at maturity.
    • Flowers May/June
    • Fruits mature in July.
    • Winged seeds ripen late August/September
    • Seeds dispersed by the wind through April. Germination usually requires exposed mineral soil..
  • Vegetative reproduction: Sprouts from the root crown if damaged or cut. Sprouting often occurs after natural disturbances such as fire.
  • The pistillate catkins emerge before or with the leaves in spring; staminate catkins are produced during the previous growing season. Cones ripen from mid-September to mid-November, depending on latitude and elevation, and seed dispersal takes place immediately thereafter.


  • Seed and seedling stock seldom available commercially, though seed are easily shaken from dried cones collected in September and October.
  • In the nursery, fresh seed should be broadcast and drilled into washed sand or a sand-humus mixture. Seedbeds should be mulched for overwinter protection with mulch removed prior to germination in the spring.
  • Spring planting requires stratification in moist sand or vermiculite for 60-90 days. Seedbeds should be kept moist and shaded until late in the summer. Two or three year-old seedlings should be used for field planting. Site preparation requires sod layer removal to prevent herbaceous competition.


  • Hardy to USDA Zone 2 (average minimum annual temperature -50ºF)
  • Good choice for wildlife plantings, disturbed site rehabilitation, and providing streambank stability and erosion control.
  • Nitrogen-fixing, symbiotic bacteria in root nodules make alder valuable for soil conditioning.
  • Can be established on cool, moist sites by direct seeding or planting 2 and 3 year-old seedlings. Nondormant seeds should be sown in the spring and dormant seeds in the fall. Unstratified seeds will germinate but at a slower rate than stratified seeds.
  • Overgrown thickets cut in the spring or winter will rapidly regrow.



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Last updated on 5 March, 2006