Perennial aquatic herb to 0.7 m long Stem: submersed, erect, rooted in substrate. Leaves: small and opposite near base, others in whorls of three, stalkless, bright green, 5 - 17 mm long, 1 - 5 mm (usually 2 mm) wide, linear to lance-oblong with a blunt tip, spreading to recurved, firm, with upper leaves densely overlapping. Flowers: either male or female, found on different plants (dioecious), with three sepals and three white and clawed petals (2 - 4.5 mm). Male flowers are surrounded by a stalked cylindrical leaflike sheath (spathe) 7 - 13.5 mm long and have 3 - 4 mm long sepals and seven to nine stamens fused at the base. When blooming, it is brought to the water surface on a stalk-like floral tube (2 - 30 cm long) formed by the joining of flower parts (hypanthium). Female flowers borne on a cylindrical spathe 8 - 20 mm long, with 2 - 3.5 mm long sepals, three styles, and a single-chambered ovary. Fruit: a leathery, egg-shaped, few-seeded capsule, opening irregularly. Seeds are 4 - 6.5 mm long and top-shaped with a 5 - 6 mm beak.
Similar species: Egeria densa has leaves in whorls of four to eight, and flowers with larger petals than Elodea canadensis. Elodea nuttallii differs by having male spathes 4 mm or shorter, male flowers separating from the plant at when blooming, female flowers with styles usually 2 mm or shorter, and limp leaves narrower than 1.7 mm with upper leaves not closely overlapping.
Flowering: mid June to mid August
Habitat and ecology: Frequent in quiet lakes, streams and ditches, and fairly tolerant to somewhat degraded water.
Occurence in the Chicago region: native
Etymology: Elodea comes from the Greek word elodes, meaning marsh. Canadensis means "from Canada."
Lower lvs small, opposite, ovate or lance-ovate, the others ternate, 6-17 נ1-5 (avg 2) mm, linear to lance-oblong, bright green, ±firm, the upper closely imbricate; fls elevated on a very slender, pedicel-like hypanthium 2-30 cm; staminate spathes 7-10+ mm (including the slender base), expanded and 2-lobed above; pistillate spathes 8-20 mm, cylindric; sep of staminate fls 3-4 mm, of pistillate fls 2-3.5 mm; pet white, clawed, 2-4.5 mm; fr turbinate, 5-6.5 mm with a 5-6 mm beak; 2n=48. In quiet water, Que. to B.C., s. to N.C., Ala., Ark., and Calif. July-Sept. (Anacharis c.; Philotria c.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.