Lemna minor

Lemna minor, the common duckweed or lesser duckweed, is a species of Lemna (duckweed) with a subcosmopolitan distribution, native throughout most of Africa, Asia, Europe and North America, occurring everywhere that freshwater ponds and slow-moving streams occur, except for arctic and subarctic climates. It is not reported as native in Australasia or South America, though is naturalised there.