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Potamogetonaceae
See list of 3 genera in this familyThe leaf sheaths in this family are usually separate from the blade and appear as stipules. For circumscription of the family, see Lindquist et al. (2006). References: Hellquist and Crow (1980), Wiegleb and Kaplan (1998).
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1a. Leaves opposite; flowers unisexual; staminate flowers with 1 stamen; stigma funnelform
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1b. Leaves alternate; flowers bisexual, with 2 or 4 stamens; stigma slender to capitate
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2a. Leaf blades narrow-linear, 0.2–1.5 mm wide, all submersed, cross-septate throughout; stipules connate to the blade for a distance of 4–30 mm, commonly more than 10 mm; spikes submersed or sometimes floating, with well-separated lower whorls of flowers, on thin, flexuous peduncles; drupes not compressed, with an indistinctly coiled embryo
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2b. Leaf blades filiform to orbicular, 0.1–75 mm wide, all submersed or some floating, cross-septate only in the central lacunar bands (if present); stipules distinct from the blade or connate for a distance of less than 10 mm (long-connate in P. robbinsii); spikes usually with contiguous whorls of flowers, on thick, stiff peduncles, usually emersed; drupes compressed, with a distinctly coiled embryo (indistinctly coiled in P. robbinsii)
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Each photo represents one genus in this family.