Potamogeton praelongus (White-stem Pondweed)
|Also known as:||Long-stalked Pondweed|
|Habitat:||part shade, sun; shallow to 20+ feet deep water; soft to hard water lakes, ponds, slow flowing rivers|
|Bloom season:||July - September|
|Plant height:||to 6+ feet|
|Wetland Indicator Status:||GP: OBL MW: OBL NCNE: OBL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Dense cylindrical spike held above the surface of the water, 1 to 3 inches (to 7.5 cm) long at the tip of the stem, sometimes arising from the upper leaf axils. Spikes have 6 to 12 whorls of flowers, each flower with a 4-parted style surrounded by 4 stamens, each stamen with a green, ladle-shaped, sepal-like appendage
Leaves and stems:
Leaves are all submersed and more or less spirally arranged along the stem; no floating leaves are produced. Blades are thin, usually bright green, lance-linear to lance-elliptic, 4 to 8 inches long, ¾ to 1½ inches (2 to 4 cm) wide, boat-shaped at the tip, the tip splitting when pressed, toothless, usually wavy along the edges, with a prominent midvein flanked by 11 to 35 lateral veins, a few which are more prominent than the rest.
Leaf bases are stalkless or clasp the stem. At the base of the leaf is a whitish, membranous appendage (stipule), not connected to the leaf blade, 1 to 4+ inches long, rounded at the tip but usually shredding later in the season. Stems are round, usually branched, straw-colored to whitish, and weakly to strongly zig-zag between the leaf nodes. Colonies may be formed from spreading rhizomes; rhizomes are stout with rusty colored spots. Vegetative buds (turions) are not produced. Glands at the leaf nodes are absent.
Fruit is a dry seed (achene), the flowering spikes forming densely packed seed heads, greenish-brown when mature.
Achenes are irregularly oval, 4 to 5.7 mm long, with a conspicuous, smooth keel along the back edge sometimes flanked by a pair of more obscure, lateral keels. The short, abrupt beak is erect.
White-stem Pondweed is fairly common in central and northeastern Minnesota, usually found in quiet, clear waters to 20+ feet deep, less often in flowing rivers. It is recognized by its pale, zig-zag stem; stalkless leaves 4 to 8 inches long, ¾ to 1½ inches (2 to 4 cm) wide, with wavy edges, 11 to 35 veins and a boat-shaped tip that splits when pressed; persistent whitish stipules 1 to 3 inches long, not attached to the leaf blade; achenes 4 to 5.7 mm long with a prominent, smooth keel along the back edge and sometimes a pair of more obscure lateral keels. Floating leaves are absent.
While there is some resemblance to the submersed leaves of other Pondweeds, the zig-zag stem, stalkless leaves with a boat-shaped tip, and no floating leaves should distinguish P. praelongus from the rest.
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- Potamogeton praelongus with a strongly zig-zag stem
- Potamogeton praelongus with a weakly zig-zag stem
- submersed plant with a whitish stem
- leaf tip is boat-shaped, splits when pressed between your fingers
- leaf veins
Photos by K. Chayka taken in Crow Wing County. Photos by Peter M. Dziuk taken in Crow Wing and Ramsey counties. Potamogeton praelongus flowering spike by Jason Hollinger, via Wikimedia Commons, used under CC BY 2.0
Have you seen this plant in Minnesota, or have any other comments about it?