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(Last Modified On 5/24/2013)
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(Last Modified On 5/24/2013)
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Family
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POTAMOGETONACEAE
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Contributor
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ROBERT R. HAYNES AND NV. ALAN WENTZ
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Description
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Plants herbaceous, glabrous, annual or perennial, aquatic in fresh, brackish, or saline waters. Stems branched or unbranched, usually dimorphic, lower stems rhizomatous and root-bearing, upper stems erect and foliaceous, the tips often hardened into winter buds. Leaves submersed and/or floating, alternate or sub- opposite, 2-ranked, entire or toothed, sessile or petiolate, stipulate, 1- to many- nerved, the stipule forming a tubular sheath around the stem, free or adnate to the leaf base, the nerves parallel, connected by perpendicular cross-veins, submersed leaves thin, linear, or lanceolate, floating leaves often leathery, lanceolate, elliptic, or ovate. Inflorescence an axillary or terminal spike or solitary or paired in leaf axils. Flowers bisporangiate or monosporangiate (plants then monoecious or less frequently dioecious), the parts arranged in 1-16-merous whorls; perianth absent or if present green, of 4-6 distinct herbaceous segments in one whorl; stamens 1-4, the anthers 1-2-celled, linear, dehiscing vertically; gynoecium of 1-16 distinct carpels, placentation apical or parietal, ovule 1, pendulous. Fruits drupaceous or achene-like, opening by decaying of the pericarp, the pericarp usually with a membranous exocarp, fleshy mesocarp, and stony endocarp; seeds
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Habit
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herb
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Description
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solitary, pendulous, the embryo straight or curved with a strongly developed hypocotyle, the endosperm absent.
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Distribution
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A family of about 8 genera and 120 species, the Potamogetonaceae are wide- spread in both hemispheres.
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Note
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Four genera, Halodule, Potamogeton, Ruppia, and Syringodium, are known to occur in Panama. Members of the family are often important or dominant components of aquatic ecosystems.
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Key
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a. Flowers monosporangiate; pollen thread-like; carpels 2; plants of saline-water habitats. b. Leaves terete or semiterete; flowers in cymes; styles divided into 2 stigmata; anthers attached at same point on filament ..... 4. Syringoclitm bb. Leaves flat; flowers solitary; styles with one stigma; anthers attached at different points on filament ...... 3. Haloclule aa. Flowers bisporangiate; pollen spherical or bilateral; carpels 4 or more (rarely 2); plants of fresh- or brackish- (rarely saline-) water habitats. c. Stamens 2; drupes stipitate; stipules adnate to the leaf base and without a free tip extending past the point of adnation; perianth absent ...... 2. Ruppia cc. Stamens 4; drupes sessile; stipules free from leaf base or if adnate then with a free tip; perianth present ...... 1. Potarnogeton
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