| General Information |
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| Distribution | A genus of about 30 species, cosmopolitan, but primarily of the Western Hemisphere, Europe, and Asia.
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| Habitat | aquatic
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Habit
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Perennial, rarely annual, aquatic or semiaquatic herbs, submersed, floating-leaved, or emerged, glabrous to sparsely pubescent, latex present; rhizomes often present, occasionally terminated by tubers; stolons often present; corms absent; tubers white to brown, smooth; roots septate.
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Leaves
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Leaves basal, submerged or emerged, sessile or petiolate; petiole terete to triangular; blade with translucent markings absent, linear to obovate, base attenuate to hastate or sagittate, margin entire, apex round to acute.
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Flowers
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Inflorescences a raceme, panicle, or rarely umbel, of 1‒17 whorls, erect, emersed or floating, rarely submersed;
bracts coarse or delicate, apex obtuse to acute, smooth or papillose proximally to distally. Flowers unisexual, the proximal rarely with ring of sterile stamens; staminate flowers pedicellate, distal to pistillate flowers; pistillate flowers mostly pedicellate, rarely sessile;
bracts subtending pedicel, lanceolate, shorter than pedicel, apex obtuse to acute; pedicel ascending to recurved; receptacle convex; sepals recurved in staminate flower, recurved to erect in pistillate flower, often sculptured, herbaceous to leathery; petals crumpled in bud, white, rarely with pink spot or tinge, entire; stamens 7‒30; filament linear to dilated,
glabrous to pubescent; pistils to 1,500 or more, spirally arranged, not radiating in starlike pattern, distinct; ovule 1, styles terminal.
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Fruit
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Fruit an aggregate of flattened achenes, with a short, erect or divergent beak, without longitudinal ribs, compressed, abaxially keeled or
not, abaxial wings and 1 curved lateral wing often present, glands present.
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Chromosomes
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x = 11.
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Notes
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The name is derived from the Latin sagitta, arrow, in reference to the leaf shape in many species.
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Contributor
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David Lorence
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