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- Potamogetonaceae
- Potamogeton
- Potamogeton gramineus
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
Native: indigenous.
Non-native: introduced (intentionally or unintentionally); has become naturalized.
County documented: documented to exist in the county by evidence (herbarium specimen, photograph). Also covers those considered historical (not seen in 20 years).
State documented: documented to exist in the state, but not documented to a county within the state. Also covers those considered historical (not seen in 20 years).
Note: when native and non-native populations both exist in a county, only native status is shown on the map.
Found this plant? Take a photo and post a sighting.
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
-
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
- unranked (S-rank: SNR)
From Flora Novae Angliae dichotomous key
11. Potamogeton gramineus L. N
grassy pondweed. Potamogeton 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.
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 → Potamogeton ×argutulus Hagstr. is a rare pondweed hybrid 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.
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).
Native to North America?
Yes
Sometimes confused with
- Potamogeton alpinus:
- submersed leaf blades mostly 4.5-18 cm long and stems unbranched (vs. P. gramineus, with the submersed leaf blades mostly 3.1-9.1 cm long and stems few to many-times branched).
Synonyms
- Potamogeton gramineus var. maximus Morong
- Potamogeton gramineus var. myriophyllus J.W. Robbins
- Potamogeton gramineus var. typicus Ogden