Alnus glutinosa (L.) Gaertn.

European alder

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New England Distribution

Adapted from BONAP data

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North America Distribution

Adapted from BONAP data

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Facts About

European alder is a 40-60 foot (15-20 m) tall tree, known for its young buds, which are sticky (hence its species name, "glutinosa"). Because its roots form relationships with nitrogen-fixing bacteria, European alder can grow in a range of otherwise infertile soils. It suckers and forms dense thickets. It has naturalized outside of plantings, and is considered potentially invasive in Connecticut.

Habitat

Anthropogenic (man-made or disturbed habitats), shores of rivers or lakes, wetland margins (edges of wetlands)

Characteristics

Habitat
  • terrestrial
  • wetlands
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • Rhode Island
  • Vermont
Growth form
the plant is a tree
Leaf type
the leaf blade is simple (i.e., lobed or unlobed but not separated into leaflets)
Leaves per node
there is one leaf per node along the stem
Leaf blade edges
the edge of the leaf blade has teeth
Leaf duration
the leaves drop off in winter (or they wither but persist on the plant)
armature on plant
the plant does not have spines, prickles, or thorns
Leaf blade length
30–90 mm
Leaf blade width
30–80 mm
Leaf stalk
the leaves have leaf stalks
Fruit type (general)
the fruit is dry but does not split open when ripe
Bark texture
  • the bark of an adult plant is ridged or plated
  • the bark of an adult plant is thin and smooth
Twig winter color
  • brown
  • gray
  • purple
  • red
Bud scale number
there are two scales on the winter bud, and their edges meet
Show All Characteristics
  • Buds or leaf scars
    Bud scale number
    there are two scales on the winter bud, and their edges meet
    Bud scar shape (Fraxinus)
    NA
    Collateral buds
    there are no collateral buds on the sides of the branches
    Leaf scar arrangement
    there is one leaf scar per node on the stem or twig
    Superposed buds
    there are no superposed buds on the branch
    Terminal bud
    the branch has a terminal bud on it
    Winter bud scale hairs
    the winter bud scales have no hairs on them
    Winter bud shape
    • the winter buds are a shape other than the choices given
    • the winter buds are ellipsoid (elliptical in three dimensions)
    Winter bud stalks
    the winter buds have short stalks
  • Flowers
    Carpels fused
    the carpels are fused to one another
    Enlarged sterile flowers
    there are no enlarged sterile flowers on the plant
    Flower appearance
    the flowers appear before the leaves
    Flower petal color
    NA
    Flower symmetry
    there are two or more ways to evenly divide the flower (the flower is radially symmetrical)
    Hairs on ovary (Amelanchier)
    NA
    Hypanthium present
    the flower does not have a hypanthium
    Inflorescence position
    the inflorescences grow on the twigs
    Inflorescence type
    the inflorescence is an ament (catkin; slender, usually pendulous inflorescence with crowded unisexual flowers)
    Number of pistils
    1
    Ovary position
    the ovary is below the point of petal and/or sepal attachment
    Petal and sepal arrangement
    the flower includes two cycles of petal- or sepal-like structures
    Petal appearance
    NA
    Petal fusion
    NA
    Sepal cilia (Ilex)
    NA
    Sepals fused only to sepals
    • NA
    • the sepals are fused to each other (not other flower parts), at least near their bases
    Stamen number
    4
    Stamen position relative to petals
    NA
    Stamens fused
    the stamens are not fused to one another
  • Fruits or seeds
    Berry color
    NA
    Fruit tissue origin
    there are no flower parts that form part of the fruit
    Fruit type (general)
    the fruit is dry but does not split open when ripe
    Fruit type (specific)
    the fruit is an achene (dry, usually 1-seeded, does not separate or split open at maturity)
    Nut with spines (Fagaceae)
    NA
    Wings on fruit
    the fruit has one or more wings on it
  • Glands or sap
    Sap color
    the sap is thick and colored
    Stalked glands on fruit (Rosa)
    NA
  • Growth form
    Growth form
    the plant is a tree
  • Leaves
    Hairs on underside of leaf blade
    • the underside of the leaf has hairs on it
    • the underside of the leaf has no hairs
    Hairs on upper side of leaf blade
    the upper side of the leaf is not hairy, or has very few hairs
    Leaf blade base shape
    • the base of the leaf blade is cuneate (wedge-shaped, tapers to the base with relatively straight, converging edges), or narrow
    • the base of the leaf blade is rounded
    Leaf blade base symmetry
    the leaf blade base is symmetrical
    Leaf blade bloom
    the underside of the leaf has no noticeable bloom
    Leaf blade edges
    the edge of the leaf blade has teeth
    Leaf blade edges (Acer)
    NA
    Leaf blade flatness
    the leaf is flat (planar) at the edges
    Leaf blade hairs
    • at least some of the hairs on the leaf blade have glands at their tips
    • the hairs on the leaf blade are different from the choices given
    Leaf blade length
    30–90 mm
    Leaf blade scales
    there are no scales on the leaf blades
    Leaf blade shape
    • the leaf blade is obovate (egg-shaped, but with the widest point above the middle of the leaf blade)
    • the leaf blade is orbicular (roughly circular, as wide as long)
    Leaf blade texture
    the leaf blade is coriaceous (has a firm, leathery texture)
    Leaf blade translucent dots
    there are no translucent dots on the leaf blade
    Leaf blade vein pattern
    the main veins of the leaf blade are pinnate (the secondary veins branch off at intervals from the main central vein) and non-arcuate (not arched towards the leaf tip)
    Leaf blade veins
    the leaf blade has one main vein running from the base toward the tip
    Leaf blade width
    30–80 mm
    Leaf duration
    the leaves drop off in winter (or they wither but persist on the plant)
    Leaf form
    the plant is broad-leaved (with broadly flattened leaf blades)
    Leaf lobe tips (Quercus)
    NA
    Leaf stalk
    the leaves have leaf stalks
    Leaf stalk attachment to leaf
    the petiole attaches at the basal margin of the leaf blade
    Leaf stalk nectaries
    there are no nectaries on the leaf stalk
    Leaf stalk shape
    the leaf stalk is not flattened
    Leaf teeth
    • the leaf blade margin is crenate (with rounded teeth) or crenulate (with tiny, rounded teeth)
    • the leaf blade margin is serrate (with forward-pointing) or dentate (with outward-pointing) with medium-sized to coarse teeth
    • the leaf blade margin is serrulate (with forward-pointing) or denticulate (with outward-pointing) with tiny teeth
    Leaf teeth hairs (Carya)
    NA
    Leaf type
    the leaf blade is simple (i.e., lobed or unlobed but not separated into leaflets)
    Leaves per node
    there is one leaf per node along the stem
    Specific leaf type
    the leaves are simple (i.e., lobed or unlobed but not separated into leaflets
    Stipules
    the plant has stipules
  • Place
    Habitat
    • terrestrial
    • wetlands
    New England state
    • Connecticut
    • Maine
    • Massachusetts
    • Rhode Island
    • Vermont
    Specific habitat
    • edges of wetlands
    • man-made or disturbed habitats
    • shores of rivers or lakes
  • Scent
    Plant odor
    the plant does not have much of an odor, or it has an unpleasant or repellant odor
  • Stem, shoot, branch
    Aerial roots
    the plant has no aerial roots
    Bark texture
    • the bark of an adult plant is ridged or plated
    • the bark of an adult plant is thin and smooth
    Branch brittleness (willows only)
    NA
    Branch cross-section
    the branch is circular in cross-section, or it has five or more sides, so that there are no sharp angles
    First-year cane (Rubus)
    NA
    Lenticels on twigs
    there are clearly lenticels on the twigs
    Pith shape
    the outline of the pith in a twig is roughly triangular
    Twig bloom
    there is no bloom on the twig
    Twig hairs
    the twigs have few or no hairs on them
    Twig papillae (Vaccinium species only)
    NA
    Twig scales
    there are no scales on the twig surface
    Twig winter color
    • brown
    • gray
    • purple
    • red
    Wings on branch
    the branch does not have wings on it
    armature on plant
    the plant does not have spines, prickles, or thorns

Wetland Status

Usually occurs in wetlands, but occasionally in non-wetlands. (Wetland indicator code: FACW)

New England Distribution and Conservation Status

Distribution

Connecticut
present
Maine
present
Massachusetts
present
New Hampshire
absent
Rhode Island
present
Vermont
present

Conservation Status

Exact status definitions can vary from state to state. For details, please check with your state.

Massachusetts
unranked (S-rank: SNR)

Native to North America?

No

Sometimes Confused With

Alnus incana:
shrubs to 10 m tall and leaf blades rounded to acute at the apex (vs. A. glutinosa, trees to 20 m tall and leaf blades rounded, retuse, or obcordate at the apex).

Synonyms

  • Alnus alnus (L.) Britt.
  • Betula alnus L. var. glutinosa L.

Family

Betulaceae

Genus

Alnus

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Information from Dichotomous Key of Flora Novae Angliae

1.  Alnus glutinosa (L.) Gaertn. E

European alder. Alnus alnus (L.) Britt.; Betula alnus L. var. glutinosa L. • CT, MA, ME, RI, VT. Pond shores, river banks, human-constructed wetlands. This species has recently (and accidentally) been planted in several human-constructed wetlands in ME. It was believed the nusery stock was Alnus incana.

1×3. Alnus glutinosa × Alnus serrulata This very rare alder hybrid is known from MA. In habit is resembles Alnus glutinosa (i.e., small trees). However, the leaf blades are rounded or sometimes shortly truncate at the apex, not showing the typical notched apex on many of the leaves.