Potamogeton zosteriformis — flat-stem pondweed
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Facts
As the name suggests, flat-stem pondweed is distinctive because of its conspicuously flattened, winged stems. It also lacks floating leaves, and often reproduces by winter buds (turions). Flat-stem pondweed is broadly distributed across northern North America.
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.
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enlargeCharacteristics
- Habitat
- aquatic
- New England state
-
- Connecticut
- Maine
- Massachusetts
- New Hampshire
- Vermont
- Leaf position
- the leaves are all submerged underwater
- Leaf arrangement
-
- alternate: there is one leaf per node along the stem
- whorled: there are three or more leaves per node along the stem
- Leaf blade length
- 100–200 mm
- Petal or sepal number
- there are four petals, sepals, or tepals in the flower
- 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
- 2–5 mm
- Fruit type (general)
-
- the fruit is dry but does not split open when ripe
- the fruit is fleshy
- Underwater leaf length
- 100–200 mm
-
Clonal plantlets
- Turion length
- 40–75 mm
-
Flowers
- 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 number
- 12–15
- 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
- 15–30 mm
- Inflorescence type
- the inflorescence is a spike (a long unbranched stem with flowers along it that lack stalks)
- Length of peduncle
- 20–50 mm
- Nectar spur
- NA
- Number of carpels
- 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 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 length
- 2–2.6 mm
- Petal number
- 4
- Petal or sepal number
- there are four petals, sepals, or tepals in the flower
- Pistil number
- 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 to petals
- the stamens are fused near the bases of the petals or tepals
- Style number
- 4
-
Fruits or seeds
- Fruit beak length
- 0.6–1 mm
- Fruit length
- 4–4.5 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
- 3–3.5 mm
-
Glands or sap
- Oil glands on nodes
-
- at least some of the nodes have pairs of oil glands
- 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
- 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
- whorled: there are three or more leaves per node along the stem
- Leaf blade length
- 100–200 mm
- Leaf blade veins
- the lateral veins are parallel or slightly arched in the direction of the tip
- Leaf blade width
- 2–5 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 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 do not forma 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
- 15–35
- Underwater leaf blade width
- 2–5 mm
- Underwater leaf length
- 100–200 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
- 0
-
Place
- Habitat
- aquatic
- New England state
-
- Connecticut
- Maine
- Massachusetts
- New Hampshire
- 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
- absent
- 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)
- New Hampshire
- extremely rare (S-rank: S1), endangered (code: E)
From Flora Novae Angliae dichotomous key
28. Potamogeton zosteriformis Fern. N
flat-stem pondweed. Potamogeton zosterifolius Schumacher ssp. zosteriformis (Fern.) Hultén • CT, MA, ME, NH, VT. Shallow, still or slow-moving, slightly acidic to basic water of lakes and rivers.
26×28. Potamogeton strictifolius × Potamogeton zosteriformis → Potamogeton ×haynesii Hellquist & Crow is a rare pondweed hybrid known from VT. It closely resembles P. strictifolius and, like that species, has light-colored, fibrous stipules and usually lacks lacunar bands on leaf blades. The hybrid also has similar winter buds to those of P. strictifolius. The hybrid shows leaf blades with 7–21 veins and rarely produces fruit. Potamogeton strictifolius has leaf blades with 3–5 (–7) veins and routinely produces fruits.
Native to North America?
Yes
Sometimes confused with
- Potamogeton epihydrus:
- floating leaves usually produced on some plants and submersed leaves with 3-13 veins, with prominent bands of lacunae on each side of the midrib (vs. P. zosteriformis, with floating leaves always absent and submersed leaves with 15-25 veins, lacking lacunae).
Synonyms
- Potamogeton zosterifolius Schumacher ssp. zosteriformis (Fern.) Hultén