The number of species is limited to 81. There are a few genera including Chara and Nitella . The oogonium that encloses the egg is capable of fossilization and records of stoneworts, the common name of this group of algae, dates back to the Silurian period, some 420 million years ago. Asexual reproduction occurs by rhizomes which extend from the lower portions of the erect plant. New apical cells and growth regions emerge from the extensions of the rhizomes.
Sexual reproduction occurs by the formation of antheridia and oogonia.
The antheridium contains filaments, whose cells give rise to flagellated sperm. The oogonium contains an egg. Both of the former structures include sterile cells that function as coverings for the gametes. Growth of the various taxa, especially Chara is generally seasonal, requiring moderate temperatures. Clear, alkaline roadside ditches with permanent water, ponds, and lakes provide ideal habitats for this alga.