Nephrophyllidium is a monotypic genus of aquatic flowering plants in the family Menyanthaceae. The sole species is Nephrophyllidium crista-galli. They are wetland plants with basal reniform and crenate leaves. Flowers are five-parted and white, and the petals are adorned with lateral wings and a midline keel. Nephrophyllidium is most nearly related to Menyanthes, which is very similar in habit. The genus name is derived from the kidney-shaped leaves (Greek: nephron = kidney and phyllon = leaf), and the specific epithet refers to the curled petal edges (Latin: crista galli = cockscomb).