1. Spirodela polyrhiza (L.) Schleid. (greater duckweed, big duckweed, duckmeat)

Pl. 98 a; Map 390

Roots 6–18 per frond. Fronds 4–8 mm long, broadly obovate to suborbicular, lacking distinct papules. Veins 5–11(–17). Turions formed late in season. Fruits 1.0–1.5 mm long. Seeds with 12–20 ribs. 2n=30, 32, 38, 50, 80.

Scattered nearly throughout the state (nearly worldwide). Floating on shallow, stagnant water of ponds, lakes, sloughs, ditches, and swamps, sometimes forming mats; also in still backwaters of streams and rivers, sometimes stranded on mud by receding waterline.