Flower:

Short, head-like cluster held above or below the surface of the water, up to ½ inch (to 13 mm) long, arising from the upper leaf axils. Spikes commonly have 3 whorls of flowers, each flower with a 4-parted style surrounded by 4 stamens, each stamen with a green to brownish, 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 flexible, green to reddish, linear, 1 to 4 inches long, 1 to 4 mm wide, rounded at the tip often with a minute point (mucronate), toothless, not wavy along the edges. The midvein is prominent with 1 to 3 narrow rows of large, empty cells (known as the lacunar band) along each side and flanked by a single pair of lateral veins.

Leaf bases are stalkless and not clasping, with a pair of greenish to yellow to orange glands .2 to 1 mm wide at the nodes. At the base of the leaf is a pale, membranous appendage (stipule), not connected to the leaf blade, blunt at the tip and not usually shredding, less than ¾ inch (to 18 mm) long but may be longer than the internodes. Stems are slightly compressed, branched, and may zig-zag somewhat between the leaf nodes. Rhizomes are mostly absent.

Numerous vegetative buds (turions), also known as winter buds, develop later in the summer at branch tips. Turions are tightly wrapped in several leaves forming a spindle-shaped structure 1¼ to 3 inches long, less than ¼ inch (to 5.1 mm) diameter, and flanked by leaves on opposite sides of the branch (2-ranked), 3 or 4 leaves per side. Turions drop off, overwinter, and form new plants the next season. Dense mats may result.

Fruit:

Fruit is a dry seed (achene), olive to brown when mature.

Achenes are irregularly oval, 2.5 to 4 mm long, usually with a low, somewhat knobby keel along the back edge, but is sometimes absent. The beak is erect and up to 1 mm long.

Notes:

Blunt-leaved Pondweed is occasional in central and northeastern Minnesota, usually found in the quiet or slow-flowing waters of lakes, ponds and rivers. It is recognized by its stalkless linear leaves 1 to 4 inches long, 1 to 4 mm wide, flexible but not wavy along the edges, 3 veins, a rounded tip sometimes with a minute point at the apex; a pair of glands at the leaf nodes; persistent pale stipules less than 1 inch long, not attached to the leaf blade and not shredding; achenes 2.5 to 4 mm long usually with (sometimes without) a low, slightly knobby keel along the back edge; spindle-shaped turions at branch tips flanked by 2-ranked leaves, 3 or 4 per side. Floating leaves are absent.

This is one of several Pondweeds with no floating leaves and linear, submersed leaves, the widest between 1 and 4 mm wide: Potamogeton foliosus lacks glands at the leaf nodes and leaves have pointed tips; P. friesii, has leaves with 5 to 7 veins and its turions have leaves that are on 2 planes (4-ranked); P. pusillus leaves have pointed tips, stipules are fused together on the lower half, and turions have 2-ranked leaves 1 to 3 per side; P. spirillus (often without floating leaves) lacks turions and stipules are attached to leaf blades for half the stipule length; P. strictifolius has stiff, straight leaves pointed at the tip and usually lacks glands at the leaf nodes; P. zosteriformis has a conspicuously flattened stem and lacks glands at the leaf nodes. P. hillii, present in Wisconsin, is also similar and has pointed or bristle tips on leaves and achenes with 3 low keels.