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Native Plant Trust: Go Botany Discover thousands of New England plants

Alnus serrulata — smooth alder

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Facts

Smooth alder has long, drooping yellow (male) catkins on a tall, suckering shrub. The leaves are finely toothed (serrulate). A fast-growing and tolerant species, hazel alder is commonly used to restore or mitigate wetlands.

Habitat

Shores of rivers or lakes, swamps, wetland margins (edges of wetlands)

New England distribution

Adapted from BONAP data

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North America distribution

Adapted from BONAP data

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Characteristics

Habitat
  • terrestrial
  • wetlands
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Rhode Island
  • Vermont
Growth form
the plant is a shrub (i.e., a woody plant with several stems growing from the base)
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
50–90 mm
Leaf blade width
35–65 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 thin and smooth
Twig winter color
  • brown
  • gray
  • red
Bud scale number
there are two scales on the winter bud, and their edges meet
Show all characteristics

  • Buds or leaf scars

    Bud position relative to scar
    the winter bud has a leaf scar just below it
    Bud scale number
    there are two scales on the winter bud, and their edges meet
    Bud scar shape (Fraxinus)
    NA
    Bundle scar number
    3
    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 distribution
    the winter buds are distributed fairly evenly along the twig
    Winter bud scale hairs
    the winter bud scales have no hairs on them
    Winter bud scales
    the winter bud is perulate (partially or completely covered with one or more scales)
    Winter bud shape
    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 appearance
    the sepals resemble leaves in color and texture
    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 clear and watery
    Stalked glands on fruit (Rosa)
    NA

  • Growth form

    Growth form
    the plant is a shrub (i.e., a woody plant with several stems growing from the base)

  • 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 fuzzy or hairy
    • 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
    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
    Leaf blade length
    50–90 mm
    Leaf blade scales
    there are no scales on the leaf blades
    Leaf blade shape
    • the leaf blade is elliptic (widest near the middle and tapering at both ends)
    • the leaf blade is obovate (egg-shaped, but with the widest point above the middle of the leaf blade)
    Leaf blade texture
    • the leaf blade is coriaceous (has a firm, leathery texture)
    • the leaf blade is herbaceous (has a leafy 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
    35–65 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 midrib glands
    the midrib of the leaf blade lacks glands on the upper surface
    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 has teeth, which themselves have smaller teeth on them
    • 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
    • New Hampshire
    • Rhode Island
    • Vermont
    Specific habitat
    • edges of wetlands
    • shores of rivers or lakes
    • swamps

  • 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 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 no lenticels on the twigs, or they are very hard to see
    Pith shape
    the outline of the pith in a twig is roughly triangular
    Pith type
    the pith inside the twig is solid, completely filled with spongy tissue
    Short shoots
    there are no peg- or knob-like shoots present
    Twig bloom
    the twig has bloom on it
    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
    • 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

Occurs only in wetlands. (Wetland indicator code: OBL)

In New England

Distribution

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

Conservation status

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

Maine
unranked (S-rank: SNR)
Massachusetts
widespread (S-rank: S5)

From Flora Novae Angliae dichotomous key

3.  Alnus serrulata (Ait.) Willd. N

smooth alder. Alnus incana (L.) Moench var. serrulata (Ait.) Boivin; A. noveboracensis Britt.; A. rugosa (Du Roi) Spreng. var. serrulata (Ait.) H.J.P. Winkl.; A. serrulata (Ait.) Willd. var. subelliptica Fern.; Betula serrulata Ait. • CT, MA, ME, NH, RI, VT. Shorelines, swamps. Variety subelliptica may represent introgressed plants with gene exchange from 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.

2×3. Alnus incana × Alnus serrulata → Alnus ×‌fallacina Callier is a rarely collected alder hybrid to be expected wherever the parental taxa co-occur. It is intermediate in morphology; however, given the slight differences between the progenitors, it is subtle and often difficult to determine (especially on herbarium sheets).

Native to North America?

Yes

Sometimes confused with

Alnus viridis:
winter buds unstalked or very shortly stalked, covered by 3-6 scales (vs. A. serrulata, with winter buds stalked, covered by 2 scales).
Alnus incana:
bark with abundant white lenticels and leaf blades with a bloom on the lower surface and lacking thin blotches of resin (vs. A. serrulata, with bark with few or no white lenticels and leaf blades usually without bloom on the lower surface and with thin blotches of resin).

Synonyms

  • Alnus incana var. serrulata (Ait.) Boivin
  • Alnus noveboracensis Britt.
  • Alnus rugosa (Du Roi) Spreng. var. serrulata (Ait.) H.J.P. Winkl.
  • Alnus serrulata var. subelliptica Fern.
  • Betula serrulata Ait.

Family

Betulaceae

Genus

Alnus