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

Epilobium hirsutum — hairy willow-herb

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Facts

Hairy willow-herb is a Eurasian native that has become an important and aggressive invader in North America. The earliest records of this plant in the Northeast date from the mid nineteenth century. It was introduced either via ships' ballast or due to cultivation in gardens. It forms dense mono-specific stands in wetlands, meadows, roadsides and waste areas. It is often found growing together with purple loosestrife (Lythrum salicaria).

Habitat

Anthropogenic (man-made or disturbed habitats), meadows and fields

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
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Rhode Island
  • Vermont
Flower petal color
  • blue to purple
  • pink to red
Leaf type
the leaves are simple (i.e., lobed or unlobed but not separated into leaflets)
Leaf arrangement
opposite: there are two leaves per node along the stem
Leaf blade edges
the edge of the leaf blade has teeth
Flower symmetry
there are two or more ways to evenly divide the flower (the flower is radially symmetrical)
Number of sepals, petals or tepals
there are four petals, sepals, or tepals in the flower
Fusion of sepals and petals
  • both the petals and sepals are separate and not fused
  • the petals or the sepals are fused into a cup or tube
Stamen number
8
Fruit type (general)
the fruit is dry and splits open when ripe
Fruit length
50–80 mm
Show all characteristics

  • Clonal plantlets

    Bulbils
    the plant does not appear to have bulbils
    Bulblets replace flowers
    there are no bulblets where the flowers are located

  • Flowers

    Anther attachment
    the anther is attached near its midpoint to the filament
    Anther color
    the anthers show no hint of a pink, reddish or purplish tint
    Anther opening
    the anthers have narrow slits or furrows that run lengthwise along the anthers
    Anther spurs
    the anthers do not have spurs on them
    Anther tube length
    0 mm
    Calyx growth after flowering
    • NA
    • the calyx does not grow to cover or partially cover the fruit
    Calyx symmetry
    there are two or more ways to evenly divide the calyx (the calyx is radially symmetrical)
    Carpels fused
    the carpels are fused to one another
    Cilia on petals
    the petal margins do not have cilia
    Cleistogamous flowers
    there are no cleistogamous flowers on the plan
    Corolla morphology
    NA
    Corolla palate
    no
    Corona lobe length
    0 mm
    Epicalyx
    the flower does not have an epicalyx
    Epicalyx number of parts
    0
    Filament surface
    the filament is smooth, with no hairs or scales
    Flower description
    the flower has an inferior ovary, with or without a hypanthium
    Flower orientation
    the flower points upwards or is angled outwards
    Flower petal color
    • blue to purple
    • pink to red
    Flower reproductive parts
    the flower has both pollen- and seed-producing parts
    Flower symmetry
    there are two or more ways to evenly divide the flower (the flower is radially symmetrical)
    Flowers sunken into stem
    no
    Form of style
    the style is lobed at the tip, and unbranched
    Fringed petal edges
    • NA
    • the petals are not fringed
    Fused stamen clusters
    NA
    Fusion of sepals and petals
    • both the petals and sepals are separate and not fused
    • the petals or the sepals are fused into a cup or tube
    Hairs on flower stalk
    the flower stalk has hairs on it
    Horns in hoods (Asclepias)
    NA
    Hypanthium
    the flower has a hypanthium
    Inflorescence one-sided
    the flowers are arrayed in a spiral around the inflorescence axis or branches, or occur singly, or in several ranks
    Inner tepals (Rumex)
    NA
    Length of flower stalk
    Up to 10 mm
    Marks on petals
    there are no noticeable marks on the petals
    Nectar spur
    the flower has no nectar spurs
    Number of branches in umbel
    0
    Number of carpels
    4
    Number of pistils
    1
    Number of sepals, petals or tepals
    there are four petals, sepals, or tepals in the flower
    Number of styles
    1
    Ovary position
    the ovary is below the point of petal and/or sepal attachment
    Perianth shape
    • the perianth is cupuliform (cup-shaped)
    • the perianth is rotate (platter-shaped, the corolla flattened, circular, with nearly horizontally spreading lobes)
    Petal and sepal arrangement
    the flower includes two cycles of petal- or sepal-like structures
    Petal and sepal colors
    • blue to purple
    • pink to red
    Petal appearance
    the petals are thin and delicate, and pigmented (colored other than green or brown)
    Petal base
    the petal narrows gradually or does not narrow at the base
    Petal folds or pleats
    the petals of the flower do not have folds or plaits
    Petal glandular dots or scales
    no
    Petal hairs (Viola)
    NA
    Petal hairs on inner/upper surface
    there are no hairs on the inner/upper petal surface
    Petal length
    10–16 mm
    Petal number
    4
    Petal shape
    the petal outline is another shape
    Petal tip shape
    the petal tip is retuse (with a blunt or rounded apex and a notch at the center)
    Petal tips (Cuscuta)
    NA
    Raceme attachment (Veronica)
    NA
    Reproductive system
    all the flowers have both carpels and stamens (synoecious)
    Scales inside corolla
    NA
    Sepal and petal color
    the sepals are different from the petals
    Sepal appearance
    the sepals are green or brown, and leaf-like in texture
    Sepal appendages (Oenothera)
    NA
    Sepal auricles
    the sepals have no auricles
    Sepal cilia
    the sepals do not have cilia
    Sepal color
    • green to brown
    • pink to red
    Sepal features
    NA
    Sepal number
    4
    Sepal orientation
    the sepals are curved outwards and downwards from the corolla
    Sepal relative length
    the sepal lobes are shorter than the fused portion
    Sepal shape
    • the sepal outline is lanceolate (lance-shaped; narrow, gradually tapering from the base to the tip)
    • the sepal outline is ovate (widest below the middle and broadly tapering at both ends)
    Sepal tip shape
    the sepal tip is acute (is sharply pointed)
    Sepal uniformity
    all the sepals are about the same size
    Sepals fused only to sepals
    • the sepals are fused to each other (not other flower parts), at least near their bases
    • the sepals are separate from one another
    Spur length
    0 mm
    Spur number
    NA
    Stamen appendages
    stamen appendages are absent
    Stamen attachment
    • the stamens are attached at or near the bases of the petals or tepals
    • the stamens are attached at or near the bases of the petals or tepals
    Stamen lengths differ
    the stamens are didynamous (two long stamens and two short ones)
    Stamen morphology
    the stamens within a cycle differ in length or width
    Stamen number
    8
    Stamen position relative to petals
    NA
    Stamen relative length
    anything
    Stamens fused
    the stamens are not attached to one another
    Staminodes
    there are no staminodes on the flower
    Stigma position
    the stigmas are positioned at the tip of the style
    Style petal-like
    the styles are not petal-like
    Style relative length
    the stigma does not protrude beyond the mouth of the corolla
    Umbel flower reproductive parts
    NA
    Upper lip of bilabiate corolla
    NA

  • Fruits or seeds

    Achene relative orientation
    NA
    Achene shape
    NA
    Achene surface (Polygonum)
    NA
    Achene type
    NA
    Berry color
    NA
    Capsule color (Viola)
    NA
    Capsule ribs
    the capsule has four prominent ribs or wings
    Capsule splitting
    the capsule splits by four main valves, teeth or pores
    Fruit (pyxis) dehiscence
    NA
    Fruit beak length
    0 mm
    Fruit cross-section
    the fruit is round in cross-section
    Fruit features (Brassicaceae)
    NA
    Fruit length
    50–80 mm
    Fruit length relative to sepals
    NA
    Fruit locules
    four
    Fruit shape
    the fruit is roughly cylindrical (with parallel sides that do not taper, and flat across the top and bottom)
    Fruit stalk orientation
    the fruits point upward or spread or curve outward
    Fruit type (general)
    the fruit is dry and splits open when ripe
    Fruit type (specific)
    the fruit is a capsule (splits along two or more seams, apical teeth or pores when dry, to release two or more seeds)
    Hair type on fruit
    the hairs on the fruits are simple (not branched), don’t have glands, and are not woolly
    Hairs on fruit
    the fruits have hairs on them
    Legumes (Fabaceae)
    NA
    Mericarp length
    0 mm
    Mericarp segment shape (Desmodium)
    NA
    Other markings on berry
    NA
    Ovary stipe
    the ovary or fruit does not have a stipe
    Ovary stipe length
    0 mm
    Placenta arrangement
    • the plant has axile placentation, in which the ovules are attached where the septa of a compound ovary are united, usually on the central axis, or to the septa themselves
    • the plant has parietal placentation, where ovules develop on the wall or slight outgrowths of the wall forming broken partitions within a compound ovary
    Relative fruit length
    0
    Rows of seeds in fruit (Brassicaceae)
    NA
    Schizocarpic fruit compression
    NA
    Schizocarpic fruit segments
    0
    Seed length
    1–1.5 mm
    Seed relative length
    the seed is longer than it is wide
    Seeds comose
    hairs are present
    Septum in fruit (Brassicaceae)
    NA
    Wings on fruit
    the fruit does not have wings on it
    prickles on fruits
    the fruits do not have thorn-like defensive structures

  • Glands or sap

    Glands on leaf blade
    the leaf blades do not have glandular dots or scales
    Sap
    the sap is clear and watery
    Sap color
    the sap is clear

  • Growth form

    Growth form
    the plant is an herb (it has self-supporting stems)
    Horizontal rooting stem
    the plant has stolons
    Lifespan
    the plant lives more than two years
    Parasitism
    the plant is not parasitic
    Plant color
    the leaves or young stems of the plant are green
    Plants darken when dry
    no
    Spines on plant
    the plant has no spines
    Underground organs
    the plant has a rhizome (a horizontal underground stem with roots growing from it)

  • Leaves

    Bracteole number (Apiaceae)
    0
    Bracteoles
    the plant has bracteoles between the primary bracts and the flowers
    Bracts in plantain (Plantago)
    NA
    Final leaf segment length (compound lvs only)
    0 mm
    Final leaf segment length to width ratio (compound lvs only)
    0
    Final leaf segment width (compound lvs only)
    0 mm
    Floral bracts
    the flower has one or more bracts associated with it
    Hairs on leaf stalk
    NA
    Hairs on underside of leaf
    the underside of the leaf is fuzzy or hairy
    Hairs on upper side of leaf
    the upper side of the leaf is fuzzy or hairy
    Hooked hairs on underside of leaf
    no
    Inflated hairs on leaf
    the leaf blade does not have inflated hairs on it
    Leaf arrangement
    opposite: there are two leaves per node along the stem
    Leaf blade base
    • the leaf has no stalk
    • the leaf has no stalk and at the base it clasps the stem
    Leaf blade base shape
    the base of the leaf blade is truncate (ends abruptly in a more or less straight line as though cut off)
    Leaf blade base symmetry
    the leaf blade base is symmetrical
    Leaf blade edges
    the edge of the leaf blade has teeth
    Leaf blade flatness
    the leaf is flat (planar) at the edges
    Leaf blade hairs
    the leaf blade has simple hairs with no glands, and not tangled or wooly
    Leaf blade length
    50–120 mm
    Leaf blade primary vein pattern
    the secondary veins branch off at intervals from the primary vein
    Leaf blade shape
    • the leaf blade is lanceolate (lance-shaped; widest below the middle and tapering at both ends)
    • the leaf blade is oblong (rectangular but with rounded ends)
    Leaf blade surface colors
    the upper side of the leaf blade is relatively uniform in color
    Leaf blade vein pattern
    the major veins of the leaf blade branch, but do not rejoin
    Leaf blade veins
    the leaf blade has one main vein running from the base towards the tip (it may or may not have secondary veins)
    Leaf blade width
    5–35 mm
    Leaf duration
    the leaves drop off in winter (or they whither but persist on the plant)
    Leaf form
    the leaves are green, with an expanded blade and a leaf-like texture
    Leaf hair orientation
    the hairs are standing up straight or curved in different directions
    Leaf sheath length
    0 mm
    Leaf shiny
    the upper side of the leaf is dull or slightly shiny
    Leaf spines
    there are no spines on the leaf edges
    Leaf stalk
    the leaves have no leaf stalks, but attach directly to the stem
    Leaf stalk attachment to leaf
    NA
    Leaf stalk base
    NA
    Leaf stalk length
    0 mm
    Leaf teeth and lobes
    the leaf blade margin has forward-pointing teeth
    Leaf tip
    the tip of the leaf blade is acute (sharply pointed)
    Leaf type
    the leaves are simple (i.e., lobed or unlobed but not separated into leaflets)
    Leaf types
    There is a gradual change in appearance of the leaves from the base (or near the base) of the plant to those from further up on the stem, with leaves progressively changing as one moves higher on the stem (often becoming shorter, or less toothed/lobed, and/or with shorter petioles).
    Leaf variation
    the leaves are nearly similar in size, prominence of teeth, and length of stalks throughout the stem
    Leaflet number
    0
    Leaflet petiolules
    NA
    Leaves per node
    there are two leaves per node along the stem
    Pinnately compound leaf type
    NA
    Specific leaf type
    the leaves are simple (i.e., lobed or unlobed but not separated into leaflets)
    Stipels
    NA
    Stipule edges
    NA
    Stipule features
    NA
    Stipule fused to leaf stalk
    NA
    Stipule length
    0 mm
    Stipule shape
    NA
    Stipules
    there are no stipules on the plant

  • Place

    Habitat
    terrestrial
    New England state
    • Connecticut
    • Maine
    • Massachusetts
    • New Hampshire
    • Rhode Island
    • Vermont
    Specific habitat
    • man-made or disturbed habitats
    • meadows or fields

  • Scent

    Plant odor
    the plant does not have much of a smell

  • Stem, shoot, branch

    Branched tendrils
    NA
    Direction of stem hairs
    the hairs point mostly upwards to outwards
    Flowering stem cross-section
    the flowering stem is circular, or with lots of small angles so that it is roughly circular
    Hair between stem nodes
    the stem has hairs between the nodes
    Hairs between stem nodes
    the hairs on the stem are plain, without glands or branches, and not tangled
    Hooked hairs on stem between nodes
    no
    Leaves on stem
    there is at least one full leaf above the base of the flowering stem
    Plant height
    50–200 cm
    Stem bloom
    there is no powdery or waxy film on the stem
    Stem hair distribution
    the hairs on the stem are distributed more of less uniformly
    Stem nodes swollen
    the stem is not swollen at the nodes
    Stem orientation
    the stems are upright or angled outwards
    Stem roughness between nodes
    the stem does not feel rough
    Stem spacing
    the plant is solitary, or a few plants are growing together
    Stem succulence
    the stems are not succulent
    Tendril origin
    NA
    Tendrils
    the plant does not have tendrils
    Wings on stem
    the stem does not have wings on it

Wetland status

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

In New England

Distribution

Connecticut
present
Maine
present
Massachusetts
present, invasive, prohibited
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.

Massachusetts
not applicable (S-rank: SNA)

From Flora Novae Angliae dichotomous key

4.  Epilobium hirsutum L. E

hairy willow-herb. CT, MA, ME, NH, RI, VT. Fields, roadsides, waste areas.

Native to North America?

No

Sometimes confused with

Epilobium parviflorum:
petals 4-9 mm long, with a deep notch, and leaves not clasping the stem (vs. E. hirsutum, with petals 10-16 mm long, with a shallow notch, and leaves somewhat clasping the stem).

Family

Onagraceae

Genus

Epilobium