Najas, the water-nymphs[3] 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,[4][5][6][7] and was often taken as constituting (by itself) the family Najadaceae.

[8] 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.

[7] An infrageneric classification of two sections is proposed: Section Americanae and sect.