Charophytes are well known to students of biology. Spirogyra, stoneworts, and desmids are all members of this fresh-water group of "green algae". The charophytes have gained even more attention recently because they are now known to be the most closely related group of organisms to the Plantae. The charophytes are in fact paraphyletic with respect to the Plantae -- some members of the group are more closely related to the plants than to the other charophytes, though there is still considerable debate as to the exact relationships among the various members.
Unlike the other green algae, the charophytes share with plants the phragmoplast method of cell division, and the asymmetric arrangement of their sperm flagella. This latter character is only observable in the Charales and Coleochaetales, since members of the remaining orders do not produce flagellated gametes as part of their life cycle.
Visit the Tree of Life for more information about the relationships of the charophytes to each other, and to the plants.