Limosella aquatica is a widespread species of flowering plant in the figwort family known by the common name water mudwort. It is native to much of the temperate world, where it grows in many types of wet habitat. It is semiaquatic, growing in moist land habitat such as meadows, in mud and wet sand next to water, and partly submersed or floating in the water. It is a fleshy annual herb forming low tufts in muddy substrate. The leaf is made up of a petiole up to long but usually quite a bit shorter, tipped with a flat spoon-shaped blade up to long. The inflorescence is an erect stalk bearing one tiny white to pink- or blue-tinted flower about wide. The fruit is a capsule up to wide containing many tiny seeds.
Limosella aquatica was given its scientific name in 1753 by Carl Linnaeus. It is part of the genus Limosella which is classified in the Scrophulariaceae family. It has two accepted varieties.
It has synonyms, one of the species and 16 of variety aquatica.