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.^{[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. Ludwigia pollen was also found associated with beetles belonging to the families Buprestidae and Scarabaeidae, suggesting that these flowers were likely pollinated by beetles rather than hymenopterans as is typical in modern species.^[2] A large number of fossil seeds of †Ludwigia collinsoniae and †L. corneri have been described from middle Miocene strata of the Fasterholt area near Silkeborg in Central Jutland, Denmark.^[3]

Listed from the NCBI database:^[4]

• Wagner, W. L., Hoch, P. C., & Raven, P. H. (2007). Revised classification of the Onagraceae. Systematic Botany Monographs, 83.

• Dressler, S.; Schmidt, M. & Zizka, G. (2014). "Ludwigia". African plants – a Photo Guide. Frankfurt/Main: Forschungsinstitut Senckenberg.