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

Myriophyllum pinnatum — cut-leaved water-milfoil

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Facts

In New England, cut-leaved water-milfoil is restricted to fresh and brackish ponds and pools along the coastal plains of Connecticut, Massachusetts and Rhode Island. It is rare and protected in these states.

Habitat

Bogs, lacustrine (in lakes or ponds), shores of rivers or lakes, swamps

New England distribution

Adapted from BONAP data

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North America distribution

Adapted from BONAP data

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Characteristics

Habitat
  • aquatic
  • wetlands
New England state
  • Connecticut
  • Massachusetts
  • Rhode Island
Leaf position
the leaves are all submerged underwater
Leaf arrangement
  • alternate: there is one leaf per node along the stem
  • whorled: there are three or more leaves per node along the stem
Leaf blade length
10–30 mm
Petal or sepal number
there are four petals, sepals, or tepals in the flower
Petal color
purple
Specific leaf type
  • the leaf is not divided, rather the blade is made up of one segment
  • the leaf is once pinnately divided and the segments are very narrow, each side providing the appearance of a comb
  • the leaf is pinnately compound (i.e., it has three or leaflets distributed along a central axis
Floating leaf shape
NA
Fruit type (general)
the fruit is dry and splits open when ripe
Underwater leaf length
10–30 mm
Show all characteristics

  • Clonal plantlets

    Turion length
    0 mm

  • Flowers

    Anther length
    0.8–1.1 mm
    Carpels fused
    the carpels are fused to one another
    Flower lower lip length
    0 mm
    Flower position
    the flowers are above the surface of the water
    Flower symmetry
    there are two or more ways to evenly divide the flower (the flower is radially symmetrical)
    Inflorescence length
    100–200 mm
    Inflorescence type
    the inflorescence is a spike (a long unbranched stem with flowers along it that lack stalks)
    Length of flower stalk
    0 mm
    Length of peduncle
    0 mm
    Nectar spur
    the flower has no nectar spurs
    Number of carpels
    4
    Ovary position
    the sepals and/or petals are attached above the ovary
    Palate on corolla
    no
    Petal and sepal arrangement
    the flower includes two cycles of petal- or sepal-like structures
    Petal appearance
    the petals are thin and delicate, and pigmented (colored other than green or brown)
    Petal color
    purple
    Petal length
    1.5–2 mm
    Petal number
    0–4
    Petal or sepal number
    there are four petals, sepals, or tepals in the flower
    Pistil number
    1
    Sepal appearance
    the sepals resemble leaves in color and texture
    Sepal number
    4
    Spur length
    0 mm
    Stamen number
    4
    Stamens fused to petals
    the stamens are not fused to the petals or tepals
    Style length
    0 mm
    Style number
    0

  • Fruits or seeds

    Fruit length
    1.3–1.8 mm
    Fruit type (general)
    the fruit is dry and splits open when ripe
    Fruit type (specific)
    the fruit is a schizocarp (when dry it splits into sections, each holding one or more seeds)

  • Glands or sap

    Oil glands on nodes
    none of the nodes have oil glands
    Sap
    the sap is clear and watery

  • Growth form

    Lifespan
    the plant lives more than two years
    Root septa
    the roots do not have transverse septa
    Roots floating in water
    there are no clusters of roots floating in the water
    Turions
    there are no turions on the plant
    Underground organs
    the plant has a rhizome (a horizontal underground stem with roots growing from it)

  • Leaves

    Bract position (Sparganium)
    NA
    Bract relative length
    At least 1380 mm
    Bracts
    the flowers or their pedicels have bracts at their bases
    Floating leaf basal lobes
    NA
    Floating leaf blade width
    0 mm
    Floating leaf length
    0 mm
    Floating leaf shape
    NA
    Floating leaf tip
    NA
    Floral bract form
    the bracts are roughly as lobed as the foliage leaves
    Floral bract length
    Up to 18 mm
    Leaf arrangement
    • alternate: there is one leaf per node along the stem
    • whorled: there are three or more leaves per node along the stem
    Leaf blade length
    10–30 mm
    Leaf blade veins
    the lateral veins radiate from the base and continue to spread away from the centerline of the leaf, or branch off the central vein at intervals
    Leaf position
    the leaves are all submerged underwater
    Leaf special features
    none of the mentioned special features are present
    Leaf-like branch segments
    8–10
    Leaf-like branch shape
    the leaf-like branches are round
    Specific leaf type
    • the leaf is not divided, rather the blade is made up of one segment
    • the leaf is once pinnately divided and the segments are very narrow, each side providing the appearance of a comb
    • the leaf is pinnately compound (i.e., it has three or leaflets distributed along a central axis
    Staminate bract edge (Myriophyllum)
    the edges of the staminate bracts have either forward-pointing teeth, or are pinnately lobed (with lobes projecting from both sides of the central axis of the leaf)
    Stipule appearance
    NA
    Stipule fused to leaf
    NA
    Stipules
    there are no stipules on the plant
    Stipules fused around stem
    NA
    Trap-bladder length
    0 mm
    Underwater leaf blade edges
    the underwater leaf blades are lobed
    Underwater leaf blade shape
    the underwater leaf blade is capillary (very fine and hair-like)
    Underwater leaf length
    10–30 mm
    Underwater leaf stalk
    yes
    Veins in floating leaf
    0

  • Place

    Habitat
    • aquatic
    • wetlands
    New England state
    • Connecticut
    • Massachusetts
    • Rhode Island
    Specific habitat
    • bogs
    • in lakes or ponds
    • shores of rivers or lakes
    • swamps

  • Stem, shoot, branch

    Flowering stem growth form
    the flowering stem is upright

Wetland status

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

In New England

Distribution

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

Conservation status

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

Connecticut
extremely rare (S-rank: S1), endangered (code: E)
Massachusetts
uncommon (S-rank: S3), special concern (code: SC)
Rhode Island
extremely rare (S-rank: S1), state threatened (code: ST)

From Flora Novae Angliae dichotomous key

6.  Myriophyllum pinnatum (Walt.) B.S.P. NC

cut-leaved water-milfoil. Myriophyllum scabratum Michx.; Potamogeton pinnatum Walt. 
• CT, MA, RI; coastal plain. Fresh or brackish ponds and pond shores, muddy or peaty pools 
and depressions.

Native to North America?

Yes and no (some introduced)

Sometimes confused with

Myriophyllum farwellii:
flowers in the axils of submersed leaves, anthers ca. 0.4 mm long, and fruits 2–2.5 mm long (vs. M. pinnatum, with flowers in emersed spikes, subtended by bract-like leaves, anthers 0.8–1.1 mm long, and fruits 1.3–1.8 mm long (vs. M. farwellii, with ).

Synonyms

  • Myriophyllum scabratum Michx.
  • Potamogeton pinnatum Walt.

Family

Haloragaceae

Genus

Myriophyllum