Myriophyllum (water milfoils; family Haloragidaceae) A genus of submerged, fresh-water aquatic herbs, with a few terrestrial species, in which the leaves are in whorls, finely pinnate when submerged and with no stipules. The flowers are in panicles or spikes held above the water and are generally very small. The fruit is usually a small dry nut, separating into 2 or 4 1-seeded nutlets. The seed has a copious endosoperm. The genus forms winter buds, which survive in the bottom of a lake or river, and from which the plant can develop in the spring. There are about 40 species, with cosmopolitan distribution.

water milfoil See MYRIOPHYLLUM.