| General Information |
| Distribution | Occurring in alkaline, subsaline, or brackish water along coasts or sometimes inland, nearly cosmopolitan, but especially common in Eurasia,
Africa, and the Americas.In the Hawaiian Islands,
indigenous to
Ni`ihau, Kaua`i, O`ahu, Moloka`i, Lana`i, Maui, Hawai`i.
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Habit
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Plants completely submerged; stems greenish to brownish, capillary or slender, terete, (2-)4-10 dm long, many-branched, arising from creeping rhizomes.
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Leaves
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Leaves all similar, well-spaced or somewhat clustered, 10-100 mm long, 0.2-0.5(-1) mm wide, apex rounded to obtuse, with an adnate, sheathing, membranous stipule at base, sheath (2-)5-20(-70) mm long, ligule ± present.
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Flowers
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Flowers 2 per peduncle, axillary, peduncles at first short, elongating up to 3 dm long in fruit, often spiralling or coiling, during anthesis the peduncles and flowers concealed by the sheath of the uppermost stem leaves, the sheath ruptured by the elongating peduncle during anthesis as the flowers move to position slightly above the water surface.
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Fruit
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Fruit symmetrical to asymmetrical, ovoid to pyriform, (1.5-)2-3(-4) mm long, the beak erect or curved, the elongate stipe 4-15(-35) mm long.
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Chromosomes
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2n = 16, 20, 24, 40
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