The role of charophytes (Charales) in past and present environments: an overview
Charophytes, i.e. extant and fossil members of the order Charales plus the members of the extinct orders Sycidiales and Moellerinales, are closely related to modern land plants. These algae have a complex morphology, and can tolerate salinities from freshwater up to hypersaline conditions, although they are not known to occur in fully marine habitats. Extant charophytes are found on all continents except Antarctica, in both lotic and lentic, natural and artificial habitats, ranging from ancient lakes to newly excavated gravel pits. The large size of the internode cells makes charophytes useful objects in plant cell biology. Charophytes can build up large biomasses in brackish and freshwater ecosystems, and contribute to a number of ecosystem services, including removal of nutrients from water, storage of carbon and nutrients in biomass and sediments, possible phytoremediation of organic chemicals and trace metal elements from water, as well as provision of habitat and food for a number of organisms. Charophytes are valuable indicators for lake and river ecological status assessment, and their oospores and gyrogonites are useful for paleolimnological reconstructions of ecosystem properties such as trophic status or salinity. This paper introduces charophytes, and summarizes different aspects studied in these macroalgae.