Charophytes
In common with other green algae and land plants, charophytes have grass green chloroplasts containing chlorophylls a and b, and store starch inside their chloroplasts. All members of the group form macroscopic branching filaments, and share a similar type of structure: a long central axis punctuated by nodal cells, each giving rise to a whorl of secondary branches. Charophyte cells are coenocytic, meaning that each contains numerous chloroplasts and nuclei; the long stems between the nodal cells may be a single cell in length. It has been suggested that this means of growth developed as an adaptation to low light, such as the bottom of lakes.
Charophytes include the genus Chara, for which the group is named, but Nitella is also very common and the two are often confused. Although the differences are subtle, distinguishing these and other Charophytes is not difficult with practice. Common habitats for these organisms are the beds of lakes (where they can form “meadows”, and indicate good water quality) and slow-flowing streams. Deterioration of water quality in lakes is commonly associated with disappearance of Charophytes, which can no longer grow in the lake bed once deprived of light by growths of other algae in the water column.
Some features of Charophyte reproduction are intriguingly close to features of land plants, such as the jacket of cells surrounding the oogonium. The ultrastructure of the flagellate sperm cells is also suggestively close to that of land plants that still retain them (such as bryophytes and ferns).
Charophyte oospores have resistant cell walls that are well known from sediment cores taken from lakes. These assist in the interpretation of past environmental conditions.
