Lemna minor

Description: Lemna minor is a floating freshwater aquatic plant, with one, two, three or four leaves each having a single root hanging in the water. As more leaves grow, the plants divide and become separate individuals. The root is 1–2 cm long. Leaves are oval, 1–8 mm long and 0.6–5 mm broad, light green, with three (rarely five) veins and small air spaces to assist flotation. It reproduces mainly vegetatively by division. Flowers are rarely produced and measure about 1 mm in diameter, with a cup-shaped membranous scale containing a single ovule and two stamens.

Flowering and Fruiting: Between late spring to early fall.

Economic Importance: L. minor is used as animal fodder, bioremediator, for wastewater nutrient recovery, and other applications. 

Reference: https://en.wikipedia.org/wiki/Lemna_minor