紫萍属（学名：Spirodela）是泽泻目天南星科浮萍亚科下的一个属。该属共有6种，分布于温带和热带地区。

Spirodela is a genus of aquatic plant. It is 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, 2-5 plants may remain connected to each other. Plants are green, but may have a red or brown underside. Multiple roots (7 to 12) emerge from each thallus. Spirodela is larger (10 mm) than Lemna (2–5 mm, one root per thallus).