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Annual herb, hydrophyte; turions absent. Fronds lanceolate to ovate, 1.5-2.0x as long as wide, 1.5-8.0 x 1-5 mm, usually pointed at apex, with 3-7 veins; adaxial surface with papillae along midvein. Roots 2-7, perforate lobe covering the point of attachment of roots. Inflorescence of 1 female and 2 male flowers enclosed in a membranous sheath; flowers and fruit occasionally present. Ovary with 1-5 ovules. Seeds ovoid, 0.8-1.0 x 0.5-0.6 mm, with 10-15 longitudinal ribs.
Roots (1--)2--7(--12), to 7 cm, all perforating scale. Fronds obovate, flat or gibbous, 1.5--8 mm, 1.5--2 times as long as wide, apex mostly pointed, upper surface without red spot; veins (3--)5--7; distinct turions absent. Flowers: ovaries 1--2-ovulate. Fruits 0.8--1 mm, laterally winged to apex. Seeds with 10--15 distinct ribs. 2n = 40, 46, 50...
Platelets to 5 × 3 mm, elliptic-obovate, ± inflated, slightly asymmetric; dorsal surface green, flat to convex; ventral surface convex, usually strong red-purple; nerves obscure. Roots 2-5. Spathe open along one side. Fruit ovoid, 1-seeded. Seed ribbed, reticulate; operculum prominent.
Like a small version of no. 1 [Spirodela polyrhiza (L.) Schleid.]; thallus 2.5–5 mm, half to 3/4 as wide, obscurely 3–5-nerved; roots 2–5; seed solitary; 2n=40, 50. Quiet water; widely scattered in warm regions, rare and irregular with us. (S. oligorhiza)
Perennial, aquatic herb, minute, floating, forming dense colonies. Roots 2-7. Fronds narrowly ovate to ovate, 1.5-2.0 x as long as wide, upper surface with papillae along the mid-vein; veins 3-7.
Aquatic herb. Plants small, floating, ldiscoid with (1-) 3-18 fairly short, clustered roots. Fronds narrow-oblong, often ringed with red.
Minute, floating aquatic forming dense colonies. Leaves purple beneath.
A herb.
