Charophyte is the common name for green plants in the order Charophyceae. This includes living plants in the family Characeae, and a number of extinct fossil families. The family Characeae has six genera: Chara, Nitella, Lamprothamnium, Tolypella, Lychnothamnus and Nitellopsis. The ones that most people will come across are in the genera Chara (also known as stoneworts), and Nitella.
Charophytes are water plants. They grow completely submerged in the water of wetlands, rivers, streams, lakes, estuaries and swamps, in fact, all sorts of non-marine watery habitats. The plant body consists of stems with whorls of ‘leaves’, anchored in the sediment by colourless rhizoids. They reproduce sexually via gametes produced by male and female reproductive organs (antheridia and oogonia, respectively), and they have seed-like oospores that germinate into the new plant. Because their reproductive organs are relatively simple they are referred to as algae, but in many ways they behave like ordinary water plants, growing from the sediment into the water and producing seeds/spores.
Charophytes are special because of their long fossil history (back the Silurian), and the fact that they are the closest living relatives to the ancestors of land plants. Many charophytes produce lime-shells around their oospores, and these lime-shells (called gyrogonites) are frequently found as fossils. Charophytes were much more diverse in prehistoric times, with many more families and genera than survive today. By studying the charophytes that exist today, we can understand what the climate and water resources of the past must have been like.
Charophytes are useful components of aquatic ecosystems. Many species require high water quality and clarity for survival, so their presence can indicate the existence of a healthy ecosystem. When they are growing they absorb nutrients and help to clarify the water. They provide habitat for invertebrates and other algae, and food for invertebrates and water birds. They harvest the energy of the sun, and make it available for other components of the food web of aquatic ecosystems. They decline when water becomes polluted, murky or eutrophic. Many places in the Northern Hemisphere that once had charophytes lost them when water quality declined. Charophytes can be restored to lakes and rivers, and their return indicates a return of healthy ecosystem function.
Charophytes are useful in physiological studies. They possess some of the largest single plant cells known, and this makes them relatively easy to manipulate for experimental studies on how cells function. Because they are related to land plants, they share many of the metabolic, electrophysical and chemical attributes of land plants, so understanding charophyte physiology can help us to understand the physiology of plants that are important to agriculture.
See Common Species for more information.