Potamogeton zosteriformis (Flat-stem Pondweed)

Plant Info
Also known as:
Family:Potamogetonaceae (Pondweed)
Life cycle:perennial
Habitat:part shade, shade, sun; shallow to 22 feet deep hard water; lakes, ponds, streams, rivers
Bloom season:July - August
Plant height:2 to 4 feet
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

Pick an image for a larger view. See the glossary for icon descriptions.

Detailed Information

Flower: Flower shape: 4-petals Flower shape: indistinct Cluster type: spike

[photo of flowers] Cylindrical spike, held above the surface of the water, ½ to 1+ inch (to 3 cm) long at the tips of branching stems. Spikes have 5 to 9 whorls of flowers, each flower with a 4-parted style surrounded by 4 stamens, each stamen with a green, paddle-shaped, sepal-like appendage.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of leaves] Leaves are all submersed with no floating leaves produced, spirally arranged, ascending to spreading, stalkless, not clasping. Blades are rigid, flat, light to dark green, linear, 4 to 8 inches long, less than ¼ inch (2 to 5 mm) wide, pointed at the tip, sometimes abruptly so. The midvein is conspicuous yellow, with 15 to 35 lateral veins.

[photo of turions and stipules] At the base of the leaf is a translucent, membranous appendage (stipule) that is white to brownish, not connected to the leaf, ½ to 1½ inches long, and becomes shredded at least at the tip. Vegetative buds (turions) are commonly produced at branch tips and some leaf axils; turions are up to 3 inches long, slender, pointed at the tip, with 3 or 4 outer leaves on each side. Glands at the leaf nodes are rarely present.

[photo of flat stem] Stems are branching, quite flat, and without spots. Plants lack rhizomes.

Fruit: Fruit type: seed without plume

[photo of fruit] Fruit is a dry seed (achene), light green to olive at maturity. Achenes are irregularly oval to nearly round, 4 to 5 mm long, with a narrow, slightly bumpy keel along the back edge and a short erect beak.


Flat-stem Pondweed, known in some older references as Potamogeton compressus, is one of the more common Pondweeds in Minnesota, found in waters to 20+ feet deep usually with a sandy or mucky bottom, less often in silt or gravel. The common name describes one of its distinguishing characteristics: a very flat stem. Of the few Pondweeds with a flat stem and linear leaves, this has the largest leaves (both length and width) than any others, 4 to 8 inches long and more than 2 mm wide, with numerous parallel veins and a pointed tip. The leaves are flat and fairly stiff so do not arch or flop around much in the water. No floating leaves are produced.

Native Plant Nurseries, Restoration and Landscaping Services ↓

Map of native plant resources in the upper midwest

  • Morning Sky Greenery - Native Prairie Plants
  • Natural Shore Technologies - Using science to improve land and water
  • Minnesota Native Landscapes - Your Ecological Problem Solvers
  • Spangle Creek Labs - Native orchids, lab propagated
  • Prairie Restorations - Bringing people together with the land

More photos

Photos by K. Chayka taken in Aikin County. Photos by Peter M. Dziuk taken in Aitkin, Cass, Crow Wing and Douglas counties.


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Joel - Stunts bay lake vermilion
on: 2022-02-01 14:16:18

Just trying to identify the weeds that engulfed the boat landing last yr. I believe it's the flat leaf pond weed.

Post a comment

Note: All comments are moderated before posting to keep the riff-raff out. An email address is required, but will not be posted—it will only be used for information exchange between the 2 of us (if needed) and will never be given to a 3rd party without your express permission.

For info on subjects other than plant identification (gardening, invasive species control, edible plants, etc.), please check the links and invasive species pages for additional resources.


Note: Comments or information about plants outside of Minnesota and neighboring states may not be posted because Id like to keep the focus of this web site centered on Minnesota. Thanks for your understanding.