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Potamogeton natans — floating pondweed

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Facts

Floating pondweed has a circumboreal distribution. It is very common in the north temperate zone and throughout New England. The shape of the floating leaves depends on the speed of the current, with faster current resulting in more elongate the leaves and less cordate leaf bases.

Habitat

Fresh tidal marshes or flats, lacustrine (in lakes or ponds), riverine (in rivers or streams), shores of rivers or lakes

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
  • wetlands
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Rhode Island
  • 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
Leaf blade length
50–200 mm
Petal or sepal number
there are four petals, sepals, or tepals in the flower
Petal color
green
Specific leaf type
the leaf is not divided, rather the blade is made up of one segment
Floating leaf shape
  • the leaf blade is elliptic (widest near the middle and tapering at both ends)
  • the leaf blade is ovate (widest below the middle and broadly tapering at both ends)
Underwater leaf blade width
0.8–2 mm
Fruit type (general)
  • the fruit is dry but does not split open when ripe
  • the fruit is fleshy
Underwater leaf length
90–200 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
    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 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
    25–50 mm
    Inflorescence type
    the inflorescence is a spike (a long unbranched stem with flowers along it that lack stalks)
    Inflorescence width
    9–12 mm
    Length of flower stalk
    0 mm
    Length of peduncle
    45–95 mm
    Nectar spur
    the flower has no nectar spurs
    Number of carpels
    1–4
    Ovary position
    the sepals and/or petals are attached below the ovary
    Palate on corolla
    no
    Petal and sepal arrangement
    the flower includes only one cycle of petals or sepals
    Petal appearance
    the petals are green and/or leafy in texture
    Petal color
    green
    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 number
    4
    Petal or sepal number
    there are four petals, sepals, or tepals in the flower
    Pistil number
    • 1
    • 4
    Sepal appearance
    NA
    Sepal length
    0 mm
    Sepal number
    0
    Sepals fused only to sepals
    NA
    Spur length
    0 mm
    Stamen number
    4
    Stamen position relative to petals
    NA
    Stamens fused
    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 number
    0–4

  • Fruits or seeds

    Fruit beak length
    0.4–0.8 mm
    Fruit length
    3.5–5 mm
    Fruit type (general)
    • the fruit is dry but does not split open when ripe
    • the fruit is fleshy
    Fruit type (specific)
    • the fruit is a drupe (fleshy, with a firm inner ovary wall that encloses a single seed)
    • the fruit is an achene (dry, usually 1-seeded, does not separate or split open at maturity)
    Fruit width
    2–3 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
    there are no turions on the plant
    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 3854 mm
    Bracts
    neither the flowers nor their pedicels have bracts
    Floating leaf basal lobes
    yes
    Floating leaf blade width
    25–60 mm
    Floating leaf length
    50–100 mm
    Floating leaf shape
    • the leaf blade is elliptic (widest near the middle and tapering at both ends)
    • the leaf blade is ovate (widest below the middle and broadly tapering at both ends)
    Floating leaf tip
    • the tip of the floating leaf blade is acute (sharply pointed)
    • the tip of the floating leaf blade is obtuse (bluntly pointed)
    • the tip of the floating leaf blade is rounded, with no point
    Floral bract form
    NA
    Floral bract length
    0 mm
    Leaf arrangement
    alternate: there is one leaf per node along the stem
    Leaf blade length
    50–200 mm
    Leaf blade veins
    the lateral veins are parallel or slightly arched in the direction of the tip
    Leaf blade width
    0.8–60 mm
    Leaf position
    • some of the leaves are floating at the surface of the water
    • 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 firm or fibrous, and colored white, green or brown
    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 form a completely closed tube around the stem
    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 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
    3–5
    Underwater leaf blade width
    0.8–2 mm
    Underwater leaf length
    90–200 mm
    Underwater leaf stalk
    yes
    Underwater leaf stalk length
    90–200 mm
    Underwater leaf tip shape
    the tip of the underwater leaf is obtuse (bluntly pointed)
    Veins in floating leaf
    17–37

  • Place

    Habitat
    • aquatic
    • wetlands
    New England state
    • Connecticut
    • Maine
    • Massachusetts
    • New Hampshire
    • Rhode Island
    • Vermont
    Specific habitat
    • fresh tidal marshes or flats
    • in lakes or ponds
    • in rivers or streams
    • shores of rivers or lakes

  • 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
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.

Maine
unranked (S-rank: SNR)
Massachusetts
widespread (S-rank: S5)

From Flora Novae Angliae dichotomous key

14.  Potamogeton natans L. N

Floating pondweed. CT, MA, ME, NH, RI, VT; throughout. Shallow, still or slow-moving, acidic to basic water of lakes and rivers, sometimes stranded on mud along tidal streams. Potamogeton natans, like many other species of pondweed, is capable of tremendous morphological variation. In still water its leaf blades are broad and subcordate at the base. 
In flowing or tidal water, the leaf blades become narrower and the bases tapered.

11×14. Potamogeton gramineus × Potamogeton natans → Potamogeton ×‌sparganiifolius Laestad. ex Fries is a rare pondweed hybrid known from NH; also reported from MA by Angelo and Boufford (2000), but specimens are unknown. It ± resembles P. oakesianus, but the submersed leaves have expanded, narrow, green blades near the apex (instead of all being phyllodial and lacking blades).

Native to North America?

Yes

Sometimes confused with

Potamogeton oakesianus:
submersed leaf blades 0.2-1 mm wide and floating leaf blades tapering to the base (vs. P. natans, with the submersed leaf blades 0.8-2 mm wide and floating leaf blades usually round to slightly cordate at the base).

Family

Potamogetonaceae

Genus

Potamogeton