Trapa natans L.

water-chestnut

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New England Distribution

Adapted from BONAP data

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North America Distribution

Adapted from BONAP data

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Facts About

Water-chestnut is an aquatic annual, native to Europe and Asia, where it is a component of many regional cuisines. Introduced in North America, it first appeared near Concord, Massachusetts in 1859. Water-chestnut can be quite invasive in the Northeast, and is classified as such in most New England states. It grows in shallow water of lakes and rivers. Control is expensive and, due to the longevity of seeds, somewhat unreliable.

Habitat

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

Characteristics

Habitat
aquatic
New England state
  • Connecticut
  • Massachusetts
  • New Hampshire
  • Vermont
Leaf position
  • some of the leaves are floating at the surface of the water
  • 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
Leaf blade length
40–60 mm
Petal or sepal number
there are four petals, sepals, or tepals in the flower
Petal color
white
Specific leaf type
the leaf is not divided, rather the blade is made up of one segment
Floating leaf shape
the leaf blade is triangular, with the stalk or attachment point on one of the sides
Underwater leaf blade width
40–80 mm
Fruit type (general)
the fruit is dry but does not split open when ripe
Underwater leaf length
40–60 mm
Show All Characteristics
  • Flowers
    Flower lower lip length
    0 mm
    Flower number
    1
    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 type
    • the flowers grow out of the axil (point where a branch or leaf is attached to the main stem)
    • the inflorescence has only one flower on it
    Nectar spur
    the flower has no nectar spurs
    Number of carpels
    2
    Ovary position
    the sepals and/or petals are attached above the ovary
    Palate on corolla
    NA
    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 hairs on inner/upper surface
    there are no hairs on the inner/upper petal surface
    Petal length
    7–10 mm
    Petal number
    4
    Petal or sepal number
    there are four petals, sepals, or tepals in the flower
    Sepal appearance
    the sepals resemble leaves in color and texture
    Sepal number
    4
    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
    Stamen number
    4
    Stamen position relative to petals
    the stamens are lined up with the sepals
    Stamens fused to petals
    the stamens are fused near the bases of the petals or tepals
    Style number
    1
  • Fruits or seeds
    Fruit length
    18–30 mm
    Fruit type (general)
    the fruit is dry but does not split open when ripe
    Fruit type (specific)
    the fruit is a nut (dry and indehiscent, with a hard wall, usually containing only one seed and usually subtended by an involucre)
    Fruit width
    20–45 mm
  • Glands or sap
    Sap
    the sap is clear and watery
  • Growth form
    Lifespan
    the plant lives only a single year or less
    Root septa
    the roots do not have transverse septa
    Underground organs
    there are only slender roots on the plant
  • Leaves
    Bract position (Sparganium)
    NA
    Floating leaf basal lobes
    no
    Floating leaf blade width
    40–80 mm
    Floating leaf length
    40–60 mm
    Floating leaf shape
    the leaf blade is triangular, with the stalk or attachment point on one of the sides
    Leaf arrangement
    • alternate: there is one leaf per node along the stem
    • opposite: there are two leaves per node along the stem
    Leaf blade length
    40–60 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
    40–80 mm
    Leaf position
    • some of the leaves are floating at the surface of the water
    • the leaves are all submerged underwater
    Leaf special features
    the leaves have inflated petioles or blades that help them float
    Leaf-like branch segments
    0
    Specific leaf type
    the leaf is not divided, rather the blade is made up of one segment
    Staminate bract edge (Myriophyllum)
    NA
    Stipules
    the plant has stipules
    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 capillary (very fine and hair-like)
    Underwater leaf blade width
    40–80 mm
    Underwater leaf length
    40–60 mm
    Underwater leaf stalk
    no
    Underwater leaf stalk length
    20–180 mm
    Underwater leaf tip shape
    the tip of the underwater leaf is acute (sharply pointed)
    Veins in floating leaf
    anything
  • Place
    Habitat
    aquatic
    New England state
    • Connecticut
    • 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)

New England Distribution and Conservation Status

Distribution

Connecticut
present, invasive, prohibited
Maine
absent
Massachusetts
present, invasive, prohibited
New Hampshire
present, invasive, prohibited
Rhode Island
absent
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)

Native to North America?

Family

Lythraceae

Genus

Trapa

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