Spirodela is a genus of aquatic plant, one of several genera containing plants commonly called duckweed. Spirodela species are members of the Araceae under the APG II system. They were formerly members of the Lemnaceae. Spirodela species are free-floating thalli; two to five plants may remain connected to each other. Plants are green, but may have a red or brown underside. Multiple roots (seven to 12) emerge from each thallus. Spirodela is larger (10 mm) than Lemna (2–5 mm, one root per thallus). Spirodela often forms floating mats with related species, e.g. Lemna and Wolffia.