Myriophyllum heterophyllum — variable-leaved water-milfoil
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Facts
Variable-leaved water-milfoil is a serious invader in New England, spreading rapidly by fragmentation, as well as by seed. Under optimum conditions, each stem may grow up to one inch per day. It is usually found first near boat launch sites, indicating that the leading means of spread may be boaters.
Habitat
Lacustrine (in lakes or ponds), riverine (in rivers or streams)
New England distribution
Adapted from BONAP data
Native: indigenous.
Non-native: introduced (intentionally or unintentionally); has become naturalized.
County documented: documented to exist in the county by evidence (herbarium specimen, photograph). Also covers those considered historical (not seen in 20 years).
State documented: documented to exist in the state, but not documented to a county within the state. Also covers those considered historical (not seen in 20 years).
Note: when native and non-native populations both exist in a county, only native status is shown on the map.
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enlargeCharacteristics
- Habitat
- aquatic
- New England state
-
- Connecticut
- Maine
- Massachusetts
- New Hampshire
- Rhode Island
- 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
- 0.4–30 mm
- Petal or sepal number
- there are four petals, sepals, or tepals in the flower
- Petal color
- white
- Specific leaf type
- the leaf is once pinnately divided and the segments are very narrow, each side providing the appearance of a comb
- Floating leaf shape
- NA
- Underwater leaf blade width
- 10–30 mm
- Fruit type (general)
- the fruit is dry and splits open when ripe
- Underwater leaf length
- 15–40 mm
-
Flowers
- Anther length
- 1–2.5 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
- 30–370 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
- 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
- white
- Petal fringed edges
- the petals are not fringed
- Petal fusion
- the perianth parts are separate
- Petal hairs on inner/upper surface
- there are no hairs on the inner/upper petal surface
- Petal length
- 1.5–3 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 length
- 1.2–2 mm
- Stamen number
-
- 0
- 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
- 1–1.5 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)
- Fruit width
- 1–1.5 mm
-
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
- 4–18 mm
- Leaf arrangement
- whorled: there are three or more leaves per node along the stem
- Leaf blade length
- 0.4–30 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 blade width
- 1.5–5 mm
- Leaf position
- the leaves are all submerged underwater
- Leaf special features
- none of the mentioned special features are present
- Leaf-like branch segments
- 5–12
- Leaf-like branch shape
- the leaf-like branches are round
- Specific leaf type
- the leaf is once pinnately divided and the segments are very narrow, each side providing the appearance of a comb
- 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 oblong (rectangular but with rounded ends)
- Underwater leaf blade width
- 10–30 mm
- Underwater leaf length
- 15–40 mm
- Underwater leaf stalk
- yes
- Underwater leaf stalk length
- 0–2 mm
- Veins in floating leaf
- 0
-
Place
- Habitat
- aquatic
- New England state
-
- Connecticut
- Maine
- Massachusetts
- New Hampshire
- Rhode Island
- Vermont
- Specific habitat
-
- in lakes or ponds
- in rivers or streams
-
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, invasive, prohibited
- Maine
- present, invasive, prohibited
- Massachusetts
- present, invasive, prohibited
- New Hampshire
- present, invasive, prohibited
- Rhode Island
- present, invasive, prohibited
- Vermont
- present, invasive, prohibited
Conservation status
Exact status definitions can vary from state to state. For details, please check with your state.
- Massachusetts
- unranked (S-rank: SNR)
From Flora Novae Angliae dichotomous key
4. Myriophyllum heterophyllum Michx. E
variable-leaved water-milfoil. CT, MA, ME, NH, RI, VT. Still or slow-moving, circumneutral to basic water of lakes and rivers.
4×Myriophyllum laxum Shuttlw. ex Chapman is a rare hybrid water-milfoil known from CT, ME. It tends to show some scattered (i.e., alternate) leaves at the base of the inflorescence (the others whorled), and the blades are often ± lobed (those of M. heterophyllum are whorled and serrulate). This hybrid could be confused with Myriophyllum pinnatum; however, the latter is smaller and has bracts that vary from pinnately lobed to prominently serrate.
Native to North America?
Yes