Aquatic and Wetland Vascular Plants of the Northern Great Plains
52. Hydrocharitaceae, the Frog's-bit Family
1. Elodea Michx. -- Waterweed2. Elodea longivaginata St. John
Stems terete, sparsely branched, 3-10 dm long. Leaves all decussate or some lower ones in whorls of 3, linear, 5-20 mm long, 0.5-2 mm wide, acute to obtuse. Spathes of male flowers 2-15 cm long, inflated near the summit, to 2.5-4 mm wide; male flowers peduncled by the threadlike hypanthium which is up to 30 cm long; sepals elliptic, 3.5-5 mm long; petals white, linear, 5 mm long; stamens 9, all attached at the summit of the hypanthium. Pistillate spathes linear-cylindric, 3-7 cm long; female flowers extended by the elongate, threadlike hypanthium which may attain lengths of several dm; sepals elliptic, 2.8 mm long; petals white, 4 mm long; stigmas entire, 1.5 mm long. Capsules ovoid, 10 mm long; seeds cylindric, 6 mm long. Jul--Aug. Prairie ponds, lakes and reservoirs; uncommon and scattered, c and w ND, e MT and e WY; (ND to Alta., s to NM and UT).
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