Zosteraceae (one of the four seagrasses families, Kubitzki ed. 1998) is a family of marine perennial flowering plants found in temperate and subtropical coastal waters, with the highest diversity located around Korea and Japan. Most seagrasses complete their entire life cycle under water, having filamentous pollen especially adapted to dispersion in an aquatic environment and ribbon-like leaves that lack stomata. Seagrasses are herbaceous and have prominent creeping rhizomes. A distinctive characteristic of the family is the presence of characteristic retinacules, which are present in all species except members of Zostera subgenus Zostera.
Zosteraceae has long been accepted by taxonomists as monophyletic. The APG II system of 2003 recognizes this family and places it in the monocot order Alismatales. The family contains approximately twenty-two species divided between two genera, Phyllospadix and Zostera totalling 22 known species (Christenhusz & Byng 2016 ). Zostera contains three subgenera: Heterozostera (formerly considered a separate genus ), Zostera and Zosterella. Zosteraceae is closely related to Potamogetonaceae, a family of freshwater aquatics.