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.

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.

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

[1] The oldest known remains of the genus are known from Eckfelder maar in Germany, dating to the Eocene.

corneri have been described from middle Miocene strata of the Fasterholt area near Silkeborg in Central Jutland, Denmark.