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

Zannichellia palustris — horned-pondweed

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Facts

Horned-pondweed in New England is most common in coastal fresh and brackish tidal waters, and occasionally in Lake Champlain, Vermont. However, it is remarkably widely distributed, being found on all continents.

Habitat

Lacustrine (in lakes or ponds), intertidal, subtidal or open ocean, 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
  • Rhode Island
  • Vermont
Leaf position
the leaves are all submerged underwater
Leaf arrangement
  • alternate: there is one leaf per node along the stem
  • opposite: there are two leaves per node along the stem
  • whorled: there are three or more leaves per node along the stem
Leaf blade length
35–42 mm
Petal or sepal number
NA
Petal color
NA
Specific leaf type
the leaf is not divided, rather the blade is made up of one segment
Floating leaf shape
NA
Underwater leaf blade width
0.2–1 mm
Fruit type (general)
the fruit is fleshy
Underwater leaf length
35–42 mm
Show all characteristics

  • Clonal plantlets

    Turion length
    0 mm

  • Flowers

    Anther color
    there is a noticeable pink, reddish or purplish tint to the anthers
    Anther length
    0.6–1 mm
    Carpels fused
    the carpel is solitary or (if 2 or more) the carpels are not fused to one another
    Flower lower lip length
    0 mm
    Flower number
    2–5
    Flower position
    the flowers are below the surface of the water
    Flower symmetry
    NA
    Inflorescence type
    • the flowers grow out of the axil (point where a branch or leaf is attached to the main stem)
    • the inflorescence is a monochasial cyme (an axis with a terminal flower, below it a branch with a terminal flower, this branch may itself have a branch and so on)
    Length of flower stalk
    0.3–1.2 mm
    Length of peduncle
    At least 0 mm
    Nectar spur
    the flower has no nectar spurs
    Number of carpels
    2–9
    Palate on corolla
    NA
    Petal and sepal arrangement
    the flower includes neither petals nor sepals
    Petal appearance
    NA
    Petal color
    NA
    Petal fringed edges
    NA
    Petal fusion
    NA
    Petal hairs on inner/upper surface
    NA
    Petal length
    0 mm
    Petal number
    0
    Petal or sepal number
    NA
    Pistil number
    • 4
    • 5
    Sepal appearance
    NA
    Sepal length
    0 mm
    Sepal number
    0
    Sepals fused only to sepals
    NA
    Spur length
    0 mm
    Stamen length
    1.6–2.1 mm
    Stamen number
    1 or 2
    Stamen position relative to petals
    NA
    Stamens fused
    • NA
    • the stamens are not fused to one another
    Stamens fused to petals
    the stamens are fused near the bases of the petals or tepals
    Style length
    0.4–0.7 mm
    Style number
    1

  • Fruits or seeds

    Fruit beak length
    0.7–2 mm
    Fruit length
    1.7–2.8 mm
    Fruit type (general)
    the fruit is fleshy
    Fruit type (specific)
    the fruit is a drupe (fleshy, with a firm inner ovary wall that encloses a single seed)
    Fruit width
    0.6–0.9 mm

  • Glands or sap

    Oil glands on nodes
    at least some of the nodes have pairs of 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
    there are only slender roots on the plant

  • Leaves

    Bract position (Sparganium)
    NA
    Bract relative length
    At least 3854 mm
    Bracts
    neither the flowers nor their pedicels have bracts
    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
    NA
    Floral bract length
    0 mm
    Leaf arrangement
    • alternate: there is one leaf per node along the stem
    • opposite: there are two leaves per node along the stem
    • whorled: there are three or more leaves per node along the stem
    Leaf blade length
    35–42 mm
    Leaf blade veins
    the lateral veins are parallel or slightly arched in the direction of the tip
    Leaf blade width
    0.2–1 mm
    Leaf position
    the leaves are all submerged underwater
    Leaf special features
    none of the mentioned special features are present
    Leaf-like branch segments
    0
    Leaf-like branch shape
    NA
    Specific leaf type
    the leaf is not divided, rather the blade is made up of one segment
    Staminate bract edge (Myriophyllum)
    NA
    Stipule appearance
    the stipules are delicate and translucent
    Stipule fused to leaf
    the stipules are not attached to the leaf blade at all
    Stipules
    the plant has stipules
    Stipules fused around stem
    the stipules do not forma closed tube around the stem
    Trap-bladder length
    0 mm
    Underwater leaf blade edges
    the underwater leaf has smooth edges, without teeth
    Underwater leaf blade shape
    the underwater leaf blade is linear (very narrow with more or less parallel sides)
    Underwater leaf blade veins
    1–3
    Underwater leaf blade width
    0.2–1 mm
    Underwater leaf length
    35–42 mm
    Underwater leaf stalk
    no
    Underwater leaf stalk length
    0 mm
    Underwater leaf tip shape
    the tip of the underwater leaf is acuminate (tapers to a long, thin point)
    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
    • intertidal, subtidal or open ocean

  • 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
present
Vermont
present

Conservation status

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

Connecticut
unranked (S-rank: SNR)
Maine
rare (S-rank: S2), special concern (code: SC)
Massachusetts
fairly widespread (S-rank: S4)
New Hampshire
extremely rare (S-rank: S1), endangered (code: E)
Vermont
extremely rare to rare (S-rank: S1S2)

var. major

Connecticut
fairly widespread (S-rank: S4)

From Flora Novae Angliae dichotomous key

1.  Zannichellia palustris L. N

horned-pondweed. Zannichellia palustris L. var. major (Hartman) Koch • CT, MA, ME, NH, RI, VT. Primarily in fresh to brackish-tidal waters, uncommonly inland in basic waters (e.g., Lake Champlain, VT).

Native to North America?

Yes

Sometimes confused with

Ruppia maritima:
leaves alternate to subopposite, mature fruits borne on stalks 12-19 mm long, and stigma capitate (vs. Z. palustris, with leaves opposite, mature fruits borne on stalks 0.3-1.2 mm long, and stigma funnelform).

Synonyms

  • Zannichellia palustris L. var. major (Hartman) Koch

Family

Potamogetonaceae

Genus

Zannichellia