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Potamogeton gramineus — grassy pondweed

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Facts

Grassy pondweed is a circumboreal species with a broad distribution in North America, and is found throughout New England. It is quite variable in appearance and can look different depending on the depth of water that its growing in. It sometimes hybridizes with various other pondweed (Potamogeton) species in New England.

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
  • 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
15–100 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
3–27 mm
Fruit type (general)
  • the fruit is dry but does not split open when ripe
  • the fruit is fleshy
Underwater leaf length
15–100 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
    15–35 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
    32–77 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
    0.3–0.5 mm
    Fruit length
    1.9–2.3 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
    1.8–2 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
    no
    Floating leaf blade width
    16–20 mm
    Floating leaf length
    35–40 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 acuminate (tapers to a long, thin 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
    15–100 mm
    Leaf blade veins
    the lateral veins are parallel or slightly arched in the direction of the tip
    Leaf blade width
    3–27 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 1440
    Underwater leaf air passage relative width
    At least 1442
    Underwater leaf air passage row number
    0–4
    Underwater leaf blade edges
    the underwater leaf has tiny, one-celled spines or points along the edge
    Underwater leaf blade shape
    the underwater leaf blade is elliptic (widest near the middle and tapering at both ends)
    Underwater leaf blade veins
    3–9
    Underwater leaf blade width
    3–27 mm
    Underwater leaf length
    15–100 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
    11–13

  • 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
widespread (S-rank: S5)

From Flora Novae Angliae dichotomous key

11.  Potamogeton gramineus L. N

grassy pondweed. Potamogeton argutulus Hagstr.; P. gramineus L. var. maximus Morong; P. gramineus L. var. myriophyllus J.W. Robbins; P. gramineus L. var. typicus Ogden • CT, MA, ME, NH, RI, VT; throughout. Shallow, still or slow-moving, acidic to basic water of lakes and rivers. The name Potamogeton argutulus has traditionally been applied to hybrids between this species and P. nodosus, but the type collection is actually P. gramineus; therefore, it is included in the synonymy of this species.

2×11. Potamogeton amplifolius × Potamogeton gramineus → This very rare pondweed hybrid is known from CT. It has sessile submersed leaves that are weakly arched and have 9–11 veins. Further, they are narrower than generally observed in Potamogeton amplifolius. The stems are unspotted.

11×13. Potamogeton gramineus × Potamogeton illinoensis → Potamogeton ×‌spathuliformis (J.W. Robbins) Morong is a rare pondweed hybrid known from CT, MA, VT. It has submersed leaves that are subsessile to petiolate, the petioles as long as 19 mm. The submersed leaves have 5–11 veins (usually 7) and have stipules 11–35 mm long.

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).

11×15. Potamogeton gramineus × Potamogeton nodosus → This rare pondweed hybrid is known from MA, ME. It has submersed leaves on petioles mostly 8–65 mm long (rarely subsessile). The submersed leaves have 7–11 veins and have stipules 13–42 mm long. It has been known by the name Potamogeton ×argutulus Hagstr., but that name is based on a collection that is actually P. gramineus.

11×16. Potamogeton gramineus × Potamogeton oakesianus → Potamogeton ×‌mirabilis Z. Kaplan, Hellquist, & Fehrer is a very rare pondweed hybrid known from NH. It is a multibranched plant that has floating leaves on mature plants like Potamogeton oakesianus, but the submersed leaves are green, narrow (mostly 0.3–1.6 mm wide), some of them with expanded green blades near the apex. This hybrid is unusual in that some leaf blades show stipules connate to the leaf blades for a distance of up to 1.2 mm (neither parent shows this character state). The spikes are 22–26 mm long.

11×19. Potamogeton gramineus × Potamogeton perfoliatus → Potamogeton ×‌nitens G. Weber is an uncommon pondweed hybrid known from CT, MA, ME, NH, VT. It ± resembles P. gramineus, but some of the leaf blades weakly clasp the stem. It is further characterized by submersed leaves 5–23 mm wide with 7–17 veins, floating leaves sometimes produced on mature plants that are 27–65 mm long and with 11–17 veins, and stipules 5–28 mm long. It is very similar to P. ×‌versicolor (7 ×19; see that nothospecies for discussion).

11×23. Potamogeton gramineus × Potamogeton richardsonii → 182 × 185. Potamogeton ×hagstroemii Benn. is a rare pondweed hybrid known from ME, VT. This hybrid has submersed leaves mostly 4–7.7 cm long with 5–9 veins. The hybrid differs from P. gramineus by its leaf blades that are convexly tapered to the base (rather than a long, straight taper to a narrow base). It differs from P. richardsonii in the +/- sessile leaves that are not cordate-clasping and submersed leaves with fewer veins.

Native to North America?

Yes

Sometimes confused with

Potamogeton alpinus:
submersed leaf blades mostly 4.5–18 cm long, red-tinged, especially in drying, stems unbranched, and drupes mostly 3–3.5 mm long, plump and turgid (vs. P. gramineus, with submersed leaf blades mostly 3.1–9.1 cm long, green, stems sparingly to many-times branched, and drupes 1.9–2.3 mm long, laterally compressed).

Synonyms

  • Potamogeton gramineus var. maximus Morong
  • Potamogeton gramineus var. myriophyllus J.W. Robbins
  • Potamogeton gramineus var. typicus Ogden

Family

Potamogetonaceae

Genus

Potamogeton