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 ( = kidney and phyllon = leaf), and the specific epithet refers to the curled petal edges ( = cockscomb). Nephrophyllidium crista-galli is found in the Pacific Northwest of America, and in Japan, where it can be called subspecies japonicum (Franch.) Yonek. & H.Ohashi. Nephrophyllidium is commonly known as deer cabbage. The IAPT determined that a prior synonym for the genus, Fauria Franch., too closely resembled the genus Faurea (Proteaceae), and thus conserved Nephrophyllidium as the accepted genus name.