SpeciesElodea schweinitzii (Planch.) Caspary
US, New York and Pennsylvania, Northampton
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 ˝ 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.
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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." Many follow Cook and Urmi-König in not accepting the taxon.
Last recorded in Pennsylvania in 1837-Ayensu, E.S. and DeFilipps, R. A. (1978). Endangered and threatened plants of the united states. Smithsonian institution and World Wildlife fund. pp 205Walter, K.S. and Gillett, H.J. (eds) (1998). 1997 IUCN Red List of Threatened Plants. Compiled by the World Conservation Monitoring Centre IUCN – The World Conservation Union, Gland, Switzerland and Cambridge, UK.