Potamogeton strictifolius (Straight-leaved Pondweed)

Plant Info
Also known as: Stiff Pondweed, Narrow-leaf Pondweed
Genus:Potamogeton
Family:Potamogetonaceae (Pondweed)
Life cycle:perennial
Origin:native
Habitat:part shade, sun; shallow to 10+ ft deep moderate to hard water; lakes, ponds, inlets
Bloom season:June - August
Plant height:1 to 3 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

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Detailed Information

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

[photo of spike just coming into bloom] Cylindrical spike, held above the surface of the water, about ½ inch (to 1.3 cm) long at the tips of branching stems and arising from some leaf axils on the upper stem. Spikes have a few to several 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

[close-up of leaf veins and tip] Leaves are all submersed with no floating leaves produced, more or less spirally arranged or 2-ranked (alternately attached on opposite sides of the stem), ascending to spreading, stalkless, not clasping. Blades are rigid, flat, straight to slightly arching, green to olive, linear, ½ to 2½ inches (to 6.3 cm) long, .6 to 2 mm wide, tapering to a sharply pointed tip or tipped with a fine bristle. The midvein is prominent and flanked by 1 or 2 pairs of lateral veins; 1 narrow row of large, empty cells (known as the lacunar band) may be along the midvein near the base but is usually absent.

[photo of developing turions] At the base of the leaf is a translucent, membranous appendage (stipule) that is white, not connected to the leaf, up to about ½ inch (7 to 15 mm) 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 nearly 2 inches (to 4.8 cm) long, slender, pointed at the tip, with 3 or 4 outer leaves on each side. Glands at the leaf nodes may or may not be present. Stems are branching and without spots. Rhizomes are absent.

Fruit: Fruit type: seed without plume

[photo of fruiting spike] Fruit is a dry seed (achene), green-brown to brown at maturity.

[photo of achenes] Achenes are oval, 2 to 3 mm long, lack any ridges and have a short erect beak.

Notes:

Straight-leaved (or Stiff-leaved) Pondweed is one of the more common Pondweeds in Minnesota, found in waters from 1 to 10+ feet deep, often with a sandy or mucky bottom. The common names are apt, as it does have fairly stiff leaves that are mostly straight.

Potamogeton strictifolius is distinguished by the combination of: no floating leaves; submersed leaves less than 3 inches long,  not more than 2 mm wide, with 3 to 5 veins, a sharply pointed or bristle tip, and mostly lacking a lacunar band except sometimes at the base of the blade; achenes 2 to 3 mm long with a short beak and lacking any ridges. Stipules are not connected to the leaf blade, are usually white and shredding, at least at the tips. I found the plant to be somewhat gangly in appearance.

There are conflicting accounts regarding glands at leaf nodes and whether the stem is round in cross-section or flattened so these traits may be variable. We'll be reviewing these in the coming seasons.

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More photos

Photos by Peter M. Dziuk taken in Wadena County.

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