Hydrocharitaceae - (tape-grass family)
This family of monocots contains more than 100 species which live in swamps or fresh water. Some species are marine. Several species are important fresh water weeds like Hydrilla verticillata or Egeria densa.
The leaves are arranged in whorls along the stem, which is often floating but may also be erect. Many species have rhizomes or stolons and can reproduce asexually by fragmentation. There are often separate male and female plants (dioecious).
For details see the respective page in Wikipedia.
The following genera and individual species are currently entered under this family: