The Charales are large, structurally complex algae found primarily in freshwater, but also in brackish, and semi-terrestrial environments. They range in size from a few millimeters to over a meter in length, and consist of a complex set of branching filaments. The Charales have an excellent fossil record extending back far over 420 million years, and two extant lineages, the Characeae and Nitellaceae, can be traced back roughly 200 million years. The Coleochaetales are microscopic but structurally complex algae found exculsively in freshwater. In some the filaments are laterally joined.
Asexual reproduction is by the formation of zoospores.
Sexual reproduction in Coleochaete is oogamous, and the zygote is retained on the parental thallus. There is reason to believe that the developing zygote obtains nutrients from the parental thallus. Like Coleochaete , the genus Chaetosphaeridium is composed of branched filaments, but the filaments enlongate and the connections between cells are so tenuous that it is often confused with colonial growth. There is reason to believe that the unicellular members of the Zygnematales are derived from filamentous ancestors. Chloroplast shape differs markedly among genera and species, and the elaborate chloroplasts are often quite beautiful.