Eel grasses (or eelgrasses) are 18-22 species of herbaceous aquatic plants. Marine plants are members of the family Zosteraceae, 12 species of which are in the genus Zostera. However, some plant systematists have treated the eel grasses as a component of a much larger family, the pondweeds or Potamogetonaceae. Freshwater species of eelgrass, which number between 6 and 10, belong to the family Hydrocharitaceae and genus Vallisneria.
Eel grasses have long, strap-like leaves that emerge from a thin rhizome growing in the surface sediment of the shallow-water, estuarine or marine wetlands of the temperate zone where these plants grow. At the end of the growing season, the dead leaves and stems of eel grass break away from the perennating (living over from season to season) rhizomes of the plant and wash up on shores in large quantities.
The flowers of eel grasses are small, either male or female, and are aggregated into an inflorescence that may be unisexual or may contain flowers of both sexes. The fruit is a small seed.
Zostera marina is a common species of marine eel grass in North America. This species is widespread in estuaries and shallow, marine bays. It is eaten by many marine invertebrates, and by swans, geese, and ducks in estuaries and other marine wetlands. During the 1930s and 1940s, a mysterious disease affected eel grass beds over much of their range. The lack of forage was hard on some species of dependent wildlife, such as the Brant goose, which declined greatly in abundance. In fact, an invertebrate known as the eel grass limpet (Lottia alvens ) became extinct at about this time. Fortunately, the eel grass beds have since recovered, and again provide critical habitat for many species of wildlife.
In the past, the large quantities of eel grass debris that often accumulate along shores in the autumn were collected and used for packing delicate objects and instruments for shipping, and for packing into the walls of houses as insulation. Today, the major economic importance of eel grasses is through the habitat and food they provide for aquatic wildlife.