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Myriophyllum verticillatum — whorled water-milfoil

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Facts

Whorled water-milfoil has a circumboreal distribution and is found in most of New England, though it is rare in the southern and western portions. The turions (overwintering buds) are distinctively club-shaped in this species. Whorled water-milfoil was used medicinally by the Iroquois as a stimulant to treat catatonic children.

Habitat

Lacustrine (in lakes or ponds), riverine (in rivers or streams)

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
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Vermont
Leaf position
the leaves are all submerged underwater
Leaf arrangement
whorled: there are three or more leaves per node along the stem
Leaf blade length
30–50 mm
Petal or sepal number
  • there are four petals, sepals, or tepals in the flower
  • there are no petals, sepals, or tepals in the flower, or they are not clearly present
Petal color
  • green
  • yellow
Specific leaf type
  • the leaf has three or more lobes distributed along a central axis
  • 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
Underwater leaf blade width
15–25 mm
Fruit type (general)
the fruit is dry and splits open when ripe
Underwater leaf length
30–50 mm
Show all characteristics

  • Clonal plantlets

    Turion length
    10–30 mm

  • Flowers

    Anther color
    there is a noticeable pink, reddish or purplish tint to the anthers
    Anther length
    2 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
    70–200 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
    Nectar spur
    the flower has no nectar spurs
    Number of carpels
    0–4
    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
    • green
    • yellow
    Petal length
    2–2.5 mm
    Petal number
    0–4
    Petal or sepal number
    • there are four petals, sepals, or tepals in the flower
    • there are no petals, sepals, or tepals in the flower, or they are not clearly present
    Pistil number
    • 0
    • 1
    Sepal appearance
    the sepals resemble leaves in color and texture
    Sepal length
    0.5–1 mm
    Sepal number
    0–4
    Sepals fused only to sepals
    the sepals are fused to each other (not other flower parts), at least near their bases
    Spur length
    0 mm
    Stamen length
    1.2–2 mm
    Stamen number
    • 0
    • 8
    Stamen position relative to petals
    NA
    Stamens fused
    the stamens are not fused to one another
    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 beak length
    0 mm
    Fruit length
    2–2.5 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
    the plant has turions
    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 much more lobed, or much less lobed, than the foliage leaves
    • the bracts are roughly as lobed as the foliage leaves
    Floral bract length
    Up to 20 mm
    Leaf arrangement
    whorled: there are three or more leaves per node along the stem
    Leaf blade length
    30–50 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 blade width
    15–25 mm
    Leaf position
    the leaves are all submerged underwater
    Leaf special features
    none of the mentioned special features are present
    Leaf-like branch segments
    9–17
    Leaf-like branch shape
    NA
    Specific leaf type
    • the leaf has three or more lobes distributed along a central axis
    • 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 air passage number
    At least 1439
    Underwater leaf air passage relative width
    At least 4336
    Underwater leaf air passage row number
    0
    Underwater leaf blade edges
    • the underwater leaf blade edges are toothed
    • the underwater leaf has smooth edges, without teeth
    Underwater leaf blade shape
    the underwater leaf blade is ovate (widest below the middle and broadly tapering at both ends)
    Underwater leaf blade width
    15–25 mm
    Underwater leaf length
    30–50 mm
    Underwater leaf stalk
    no
    Underwater leaf stalk length
    0 mm
    Underwater leaf tip shape
    the tip of the underwater leaf is obtuse (bluntly pointed)
    Veins in floating leaf
    0

  • Place

    Habitat
    aquatic
    New England state
    • Connecticut
    • Maine
    • Massachusetts
    • New Hampshire
    • Vermont
    Specific habitat
    • in lakes or ponds
    • in rivers or streams

  • Stem, shoot, branch

    Flowering stem growth form
    the flowering stem trails along the substrate, or floats in the water

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
absent
Vermont
present

Conservation status

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

Connecticut
unrankable (S-rank: SU)
Massachusetts
extremely rare (S-rank: S1), endangered (code: E)
New Hampshire
unrankable (S-rank: SU), Ind (code: Ind)
Vermont
rare to uncommon (S-rank: S2S3)

From Flora Novae Angliae dichotomous key

10.  Myriophyllum verticillatum L. N

whorled water-milfoil. Myriophyllum verticillatum L.  var. intermedium W.D.J. Koch; M. verticillatum L. var. pectinatum Wallr. • CT, MA, ME, NH, VT; generally becoming rare in southern and western New England. Slow or still-moving, circumneutral to basic water of lakes and rivers.

Native to North America?

Yes

Sometimes confused with

Myriophyllum aquaticum:
flowers subtended by bracts mostly 25–35 mm long with uniform linear divisions 4–8 mm long, the bracts +/- similar in size and division to the submersed leaves, and submersed leaves with petioles 5–7 mm long (vs. M. verticillatum, with flowers subtended by bracts less than 15 mm long, with marginal teeth or divisions shorter than 4 mm, the bracts conspicuously reduced in size and less divided than the submersed leaves, and submersed leaves with petioles 0–2 mm long).
Myriophyllum spicatum:
lower bracts of inflorescence less than 2 times as long as the flowers or fruits, upper bracts of inflorescence entire to minutely toothed (vs. M. verticillatum, with lower bracts of inflorescence 2 or more times as long as the flowers or fruits, prominently toothed to lobed, upper bracts of inflorescence toothed to lobed).

Synonyms

  • Myriophyllum verticillatum var. intermedium W.D.J. Koch
  • Myriophyllum verticillatum var. pectinatum Wallr.

Family

Haloragaceae

Genus

Myriophyllum