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Potamogeton obtusifolius — blunt-leaved pondweed

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Facts

Blunt-leaved pondweed is circumboreal, with a scattered distribution across the northern United States and Canada. It is more common in New York and New England. It is one of the submersed species, lacking floating leaves, and the submersed leaves are distinctively linear, obtuse to rounded at the apex, and with delicate stipules.

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
alternate: there is one leaf per node along the stem
Leaf blade length
30–82 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
NA
Underwater leaf blade width
1–3.5 mm
Fruit type (general)
  • the fruit is dry but does not split open when ripe
  • the fruit is fleshy
Underwater leaf length
30–82 mm
Show all characteristics

  • Clonal plantlets

    Turion length
    35–78 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
    8–13 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
    Length of peduncle
    8–42 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
    0.6–0.7 mm
    Fruit length
    2.5–3.5 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
    1.7–2.4 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
    the plant has turions
    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
    Leaf blade length
    30–82 mm
    Leaf blade veins
    the lateral veins are parallel or slightly arched in the direction of the tip
    Leaf blade width
    1–3.5 mm
    Leaf position
    the leaves are all submerged underwater
    Leaf special features
    none of the mentioned special features are present
    Leaf-like branch segments
    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 form a completely closed tube around the stem
    Trap-bladder length
    0 mm
    Underwater leaf air passage number
    At least 1440
    Underwater leaf air passage relative width
    At least 1442
    Underwater leaf air passage row number
    1–3
    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
    Underwater leaf blade width
    1–3.5 mm
    Underwater leaf length
    30–82 mm
    Underwater leaf stalk
    no
    Underwater leaf stalk length
    0 mm
    Underwater leaf tip shape
    • the tip of the underwater leaf is obtuse (bluntly pointed)
    • 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 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.

Massachusetts
extremely rare (uncertain) (S-rank: S1?)
New Hampshire
historical (S-rank: SH), endangered (code: E)
Vermont
uncommon (S-rank: S3)

From Flora Novae Angliae dichotomous key

17.  Potamogeton obtusifolius Mert. & Koch N

blunt-leaved pondweed. CT, MA, ME, NH, RI, VT. Shallow, still or slow-moving, circumneutral 
to basic water of lakes and rivers.

Native to North America?

Yes

Sometimes confused with

Potamogeton berchtoldii:
leaves 0.2-2.5 mm wide, acutely to obtusely pointed at the apex, and green (vs. P. obtusifolius, with leaves 1-3.5 mm wide, rounded to obtusely pointed at the apex, and usually suffused with red).

Family

Potamogetonaceae

Genus

Potamogeton