Stuckenia vaginatus

Perennial submersed aquatic herb with rhizomes 20 cm - 0.5 m tall Stem: freely branched. Leaves: submersed, alternate, stalkless, opaque, 1 - 10 cm long, to 3 mm wide, thread-like to linear with a tapering base and blunt, rounded, or slightly notched tip, typically one-veined, channeled, plump. Stipules adhered to base of leaf blade for two-thirds or more their length, 2 - 9 cm long, sheaths inflated three to five times the width of the stem. Inflorescence: an upright, bead-like spike with three to twelve whorls of flowers, submersed, 1 - 8 cm long, on a terminal stalk. Stalk slender, 3 - 15 cm long, flexible. Flowers: greenish, tiny. Stamens four. Anthers two-chambered, with four edge-to-edge sepal-like outgrowths. Pistils four. Fruit: an achene, brown, 3 - 3.8 mm long, 2 - 3 mm wide, obliquely reverse egg-shaped, plump, with an inconspicuous beak.

Similar species: Pondweeds in the genus Potamogeton are similar to those of Stuckenia, but the submersed leaves of Potamogeton are translucent, flat, and lack channels, whereas those of Stuckenia are opaque, channeled, and plump. Compare the inflated stipule sheaths of this species with S. pectinatus to best distinguish between the two.

Habitat and ecology: Rare in the Chicago Region. A single specimen was collected just offshore of a lake in Cook County, Illinois.

Occurence in the Chicago region: native

Etymology: Vaginatus means "with a sheath."

Author: The Morton Arboretum