Najas, the water-nymphs or naiads, is a genus of aquatic plants. It is cosmopolitan in distribution, first described for modern science by Linnaeus in 1753. Until 1997, it was rarely placed in the Hydrocharitaceae, and was often taken as constituting (by itself) the family Najadaceae. The APG II system, of 2003 (unchanged from the APG system, of 1998), places the genus in family Hydrocharitaceae, in the order Alismatales of the monocots.