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

Ceratophyllum demersum — common hornwort, coontail

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Facts

Common hornwort has a worldwide distribution and is common throughout New England. It can form large, monospecific stands in lakes and slow-moving streams. It spreads mainly vegetatively, so it is the least likely hornwort (Ceratophyllum) to be found in fruit.

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
  • 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
10–30 mm
Petal or sepal number
there are seven or more petals, sepals, or tepals in the flower
Petal color
NA
Specific leaf type
  • the leaf is divided into two equal parts; these parts may also be divided into two further parts
  • the leaf is not divided, rather the blade is made up of one segment
  • the leaf is palmately compound (i.e., it has two or more leaflets radiating from a common point)
  • 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
15–60 mm
Fruit type (general)
the fruit is dry but does not split open when ripe
Underwater leaf length
10–30 mm
Show all characteristics

  • Clonal plantlets

    Turion length
    0 mm

  • Flowers

    Anther length
    1–1.1 mm
    Carpels fused
    NA
    Flower lower lip length
    0 mm
    Flower number
    1
    Flower position
    the flowers are below 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
    Inflorescence width
    1–3 mm
    Length of flower stalk
    0–1 mm
    Length of peduncle
    0–1 mm
    Nectar spur
    the flower has no nectar spurs
    Number of carpels
    0–1
    Ovary position
    the sepals and/or petals are attached below the ovary
    Palate on corolla
    NA
    Petal and sepal arrangement
    the flower includes only one cycle of petals or 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
    there are seven or more petals, sepals, or tepals in the flower
    Pistil number
    • 0
    • 1
    Sepal appearance
    the sepals resemble leaves in color and texture
    Sepal length
    1.5–2 mm
    Sepal number
    7–15
    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 number
    • 0
    • 10
    • 11
    • 12
    • 13 or more
    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
    4.5–6 mm
    Style number
    0–1

  • Fruits or seeds

    Fruit length
    3.5–6 mm
    Fruit type (general)
    the fruit is dry but does not split open when ripe
    Fruit type (specific)
    the fruit is an achene (dry, usually 1-seeded, does not separate or split open at maturity)
    Fruit width
    2–4 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
    NA
    Roots floating in water
    NA
    Turions
    there are no turions on the plant
    Underground organs
    NA

  • Leaves

    Bract position (Sparganium)
    NA
    Floating leaf basal lobes
    NA
    Floating leaf blade width
    0 mm
    Floating leaf length
    0 mm
    Floating leaf shape
    NA
    Floating leaf tip
    NA
    Leaf arrangement
    whorled: there are three or more leaves per node along the stem
    Leaf blade length
    10–30 mm
    Leaf blade width
    15–60 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
    the leaf-like branches are flat
    Specific leaf type
    • the leaf is divided into two equal parts; these parts may also be divided into two further parts
    • the leaf is not divided, rather the blade is made up of one segment
    • the leaf is palmately compound (i.e., it has two or more leaflets radiating from a common point)
    • the leaf is pinnately compound (i.e., it has three or leaflets distributed along a central axis
    Staminate bract edge (Myriophyllum)
    NA
    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 blade edges are toothed
    Underwater leaf blade shape
    • the underwater leaf blade is flabellate (fan-shaped)
    • the underwater leaf blade is linear (very narrow with more or less parallel sides)
    Underwater leaf blade width
    15–60 mm
    Underwater leaf length
    10–30 mm
    Underwater leaf stalk
    no
    Underwater leaf stalk length
    0 mm
    Underwater leaf tip shape
    the tip of the underwater leaf is rounded, with no 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

  • 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.

Massachusetts
widespread (S-rank: S5)

From Flora Novae Angliae dichotomous key

1.  Ceratophyllum demersum L. N

common hornwort. Ceratophyllum apiculatum Cham. • CT, MA, ME, NH, RI, VT; throughout. 
Lakes and slow-moving streams.

Native to North America?

Yes

Sometimes confused with

Ceratophyllum echinatum:
leaves mostly 3-times or 4-times forked and achenes with 2 basal spines and 2-13 lateral spines (vs. C. demersum, with leaves mostly 1-time or 2-times forked and achenes with only 2 basal spines).

Synonyms

  • Ceratophyllum apiculatum Cham.

Family

Ceratophyllaceae

Genus

Ceratophyllum