Water fern of Europe and Asia and the eastern United States distinguished by four leaflets resembling clover leaves WordNet 3.0 & Open English WordNet

Marsilea quadrifolia is a herbaceous plant found naturally in central and southern Europe, Caucasia, western Siberia, Afghanistan, south-west India, China, Japan, and Vietnam, though it is considered a weed in some parts of the United States, where it has been well established in the northeast for over 100 years. Wikipedia