Ludwigia (primrose-willow, water-purslane, or water-primrose) is a genus of about 75 species of aquatic plants with a cosmopolitan but mainly tropical distribution. At current, 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 Carolus Linnaeus after Christian Gottlieb Ludwig (1709-1773), a German botanist, who was apparently not amused by this honour.

Ludwigia octovalvis commonly known as Mexican Primrose-willow is an exotic perennial subshrub from Hawaii. The flowers emerge singly from the leaf axils and stem tips and have 4 broad, yellow, often notch-tipped petals and 4 green, lance-shaped or egg-shaped sepals. The flowers are followed by elongated, cylindrical, 8-ribbed seed capsules tipped with 4 calyx lobes (the former sepals). The leaves are green, alternate, and lance-shaped to narrowly egg-shaped. The stems are green to sometimes brownish and woody at the base, upright, well-branched, and variably hairy.