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Roots (1--)2--21 per frond, abaxial surface at node. Fronds floating (only turions sink to bottom), 2--10, coherent in groups, each obovate-circular, flat or gibbous, 1.5--10 mm, margins entire; air spaces in tissue; reproductive pouches 2, lateral, at base from which daughter fronds and flowers originate, triangular; veins (3--)5--16(--21), from point in proximal part of frond (node); small bifid 2-cleft membranous scale (interpreted as prophyllum) enveloping base of frond, covering point of attachment of roots; anthocyanins present (especially on abaxial surface); pigment cells present (visible in dead fronds as brown dots); turions present or absent, brownish olive, circular-reniform, smaller than growing frond. Flowers 1(--2) per frond, surrounded by small utricular, membranous scale; stamens 2, 4-locular. Seeds 1--3, longitudinally ribbed. x = 10, 18, 23.
Fronds free floating, 1-10 individuals coherent together, shiny green on upper surface, usually red on lower surface, outline usually asymmetric, flat on upper surface, rarely slightly gibbous on lower surface; 2 lateral pouches for reproducing daughter fronds and flowers present at base, bases of pouches surrounded by a small membranous scale covering bases of roots; veins 7-16(-21), splitting from node toward apex, sometimes visible on upper surface. Pigment cells present (visible in dried fronds as brown dots). Roots (5-)7-21, surrounded by a tubular sheath at base, enclosed by a rounded to pointed cap at apex. Daughter fronds connected to mother frond by a thin white stipe. Flower surrounded by a small, utricular, membranous scale with a narrow opening at apex; stamens 2, 4-locular. Seeds 1-3, ribbed longitudinally.
Floating aquatics. Thallus discoid to oblong, 3–10 mm. long, 1.2–8 mm. wide. Daughter thallus budding from lateral slit, remaining attached to parent by slender stipe, several individuals often connected. Roots 2– numerous, usually from swollen portion beneath thallus; root-cap acute. Turions (resting buds) produced in adverse conditions. Flowers rarely produced, unisexual; spathe enclosing 2–3 ♂ and 1 ♀ flowers in lateral slit pouch; ♂ flowers each with 1 stamen; pistillate flower bearing 1–4 ovules.
Thallus flat or slightly convex on both sides, usually somewhat asymmetrical, marked with 3–15 obscure to evident nerves diverging from a nodal point near the base; roots 2–12+, descending from the nodal point, each with a single vascular strand; reproductive pouches 2, lateral, opposite the nodal point; infl (seldom produced) in one of the lateral pouches, with 2 staminate fls and one pistillate, collectively subtended by a tiny spathe; anther bilocular; ovules 1–4. 4, cosmop.
Plants floating on water surface, budding from lateral pouches, 3-5 or more platelets remaining attached together. Platelets orbicular to obovate in outline, pigmented red-purple on one or both surfaces, ± asymmetric, nerves absent or present. Roots 2-15 in a group. Inflorescence in lateral pouch, enclosed in spathe. Ovules 1-4. Fruit slightly winged. Seed longitudinally ribbed and transversely striate or smooth. Spp. 6, mostly widespread. Adventive sp. 1.
Fronds floating on water surface (only turions sinking to bottom), 2–few cohering in small groups; margins entire; nerves (3–) 5–21; frond base surrounded by a small scale covering the point of attachment of the roots. Roots (1–) 2–21 per frond.
