Ludwigia (primrose-willow, water-purslane, or water-primrose) is a genus of about 82 species of aquatic plants with a cosmopolitan but mainly tropical distribution.

Currently (2023), there is much debate among botanists and plant taxonomists as to the classification of many Ludwigia species. Botanists from the US Department of Agriculture are currently doing genetic analyses on plants from the Western US and South America to better classify members of this genus.

The genus was named by Carl Linnaeus after Christian Gottlieb Ludwig (1709-1773).

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