Plants perennial, of fresh waters. Rhizomes and stolons absent. Erect stems rooted in substrate, branched or unbranched, elongate. Leaves cauline, whorled, 3--7 at each node, or leaves opposite at 4+ proximalmost nodes, submersed, sessile; blade linear to linear-lanceolate, apex acute; midvein without lacunae along side(s), blade uniform in color throughout;; abaxial surfacely without prickles or aerenchyma; intravaginal squamules entire. Inflorescences solitary, sessile; spathes not winged. Flowers unisexual, staminate and pistillate on different plants, or rarely bisexual, usually projected to surface of water by elongate floral tube base, sessile; petals white. Staminate flowers: filaments distinct or 3 inner connate ½ their length; anthers oval; pollen in monads or tetrads. Pistillate flowers: ovary 1-locular; styles 3, not 2-fid. Fruits ovoid to lance-ellipsoid, smooth, dehiscing irregularly. Seeds cylindric to fusiform, glabrous to hirsute. An additional name, Elodea schweinitzii (G. Planchon) Caspary, has appeared in North American literature. Although it was accepted by some (H. St. John 1965), others stated, 'Elodea schweinitzii is something of a taxonomist's nightmare' (C. D. K. Cook and K. Urmi-König 1985). The few collections referable to the name are exceedingly variable, so variable in fact that the authors added, 'the main character is variability itself.' I am following Cook and Urmi-König in not accepting the taxon.
Plants perennial, of fresh waters. Rhizomes and stolons absent. Erect stems rooted in substrate, branched or unbranched, elongate. Leaves cauline, in whorls of 5 or more [opposite], submersed, sessile; blade linear, base sloping to stem, apex obtuse; midvein without rows of lacunae along side(s), blade uniform in color throughout;; abaxially surface without prickles or aerenchyma; intravaginal squamules entire. Inflorescences 1-flowered, sessile; spathes not winged. Flowers unisexual, staminate and pistillate on different plants, projected to surface by slender, elongate floral tube base, pedicellate; petals white. Staminate flowers: filaments distinct; anthers linear; pollen in monads. Pistillate flowers: ovary 1-locular; styles 3, not 2-fid. Fruits ovoid, smooth, dehiscing irregularly. Seeds fusiform, mucilaginous.
Fls unisexual (and the plants dioecious) or seldom perfect, borne singly in submersed, sessile or subsessile, axillary, bidentate or bifid spathes, elevated to the surface of the water on a long, slender, pedicel-like hypanthium (or the staminate fls sessile, breaking loose, and floating); fls ephemeral and delicate; pet white or purple, not much (if at all) longer than the sep, or wanting; no nectaries; staminate fls with typically 9 stamens, an outer cycle of 6 distinct, an inner cycle of 3 with the filaments evidently connate below, the filaments shorter than the explosively dehiscent, eventually explanate anthers; pollen floating; pistillate fls with 3 staminodia, and an elongate style with 3 slender, simple or often bifid stigmas; ovules few, parietal or nearly basal; fr capsular; submersed aquatic perennials, rooted to the bottom or free-drifting when broken loose; stems simple or sparsely branched; lvs all cauline, sessile, slender, minutely and sharply serrulate, 1-nerved, at least the middle and upper opposite or whorled; stipules minute, evanescent. (Anacharis, Philotria) 5, New World. E. schweinitzii (Planch.) Casp., with perfect fls and 3 stamens, originally native apparently to s. N.Y. and e. Pa., has not been recollected since 1832 and is apparently extinct. It may reflect hybridization between E. canadensis and E. nuttallii.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Much like Elodea, but the fls more showy, nectariferous, and insect- pollinated; pet much longer than the sep; dioecious; fls of both sexes elevated to the surface by the slender, pedicel-like hypanthium; staminate spathes 2-4-fld; staminate fls with 9 distinct stamens and a small central nectary; filaments elongate; anthers short, each pollen-sac opening longitudinally, not explosive; pistillate spathes split half way down one side; style deeply trifid, each segment deeply 2-3-cleft and with a small nectary externally at the base of each lobe; lower lvs opposite or ternate, the others in whorls of 4-8. 2, S. Amer.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.