Flower:

Loose cylindrical spike 1¾ to 4½ inches (4.5 to 11.4 cm) long, usually produced under water at branch and stem tips. Spikes have 3 to 5 whorls of flowers, each flower with a 4-parted style surrounded by 4 stamens, each stamen with a green to brown sepal-like appendage.

Leaves and stems:

Leaves are submersed, alternate; no floating leaves are produced. Blades are flexible, linear, 1 to 4 inches (3 to 10 cm) long, .5 to 1.5 mm wide, 1-veined, tapering to a pointed tip (sometimes abruptly so), stalkless. 

At the base of the leaf is a leaf-like appendage (stipule), connected to the leaf blade (adnate) for up to 1 inch (1 to 3 cm) and at least 2/3 its length, the tip membranous and free from the blade for 2 to 10 mm. Stems are round to slightly compressed in cross-section, branched, and may zig-zag somewhat between the nodes. Branches are often very leafy in a fan-like arrangement, especially on the upper stem.

Colonies form from rhizomes that end in a white tuber, from which a new plant sprouts.

Fruit:

Fruit is a dry seed (achene), yellow-brown to brown when mature, oval to egg-shaped, 3 to 4.5 mm long, with a short beak.

Along the back edge is usually a low smooth keel; a pair of low, lateral ridges may also be present, though any or all of these can be obscure.

Notes:

Sago Pondweed has a world-wide distribution and is one of the most common aquatics in Minnesota, found in either the quiet or slow-moving waters of lakes and ponds as well as the flowing waters of rivers and streams. Both the tubers and fruit are very important food for aquatic wildlife, ducks in particular.

It is recognized by leaves that are linear, stalkless, 1 to 4 inches (to 10 cm) long, about 1 mm wide, flexible, 1-veined, tapering to a pointed tip, sometimes abruptly so; long stipules connected to the blade (adnate) for 2/3 to nearly their entire length, the membranous tip free from the blade; flower/fruit cluster a spike with 2 to 5 whorls; achenes 3 to 4.5 mm long usually with (sometimes without) a low smooth keel along the back edge and/or a pair of low lateral ridges; rhizomes ending in a white tuber. Floating leaves are absent, though in shallow water the submersed leaves may float on the surface.

Adnate stipules are a trait common to Stuckenia, with S. pectinata being the most common of the 3 species in Minnesota. S. filiformis leaves are rounded, blunt or notched at the tip, up to 6 inches (15 cm) long and 2 mm wide, and achenes are smaller, 2 to 3 mm long with an obscure beak. S. vaginata, rare in Minnesota, has large, inflated stipules, leaf tips are blunt or notched at the tip, and achenes are 3 to 3.5 mm long. While some Potamogeton Pondweeds have adnate stipules, they are attached to the leaf for less than half their length where those of Stuckenia are attached for at least 2/3 their length.