Flower:

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:

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.

Notes:

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.