Chlorophyceae
The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology.The chloroplast may be discoid, plate-like, reticulate, cup-shaped, spiral- or ribbon-shaped in different species.Depending on the species, Chlorophyceae can grow unicellular (e.g. Chlamydomonas), colonial (e.g. Volvox), filamentous (e.g. Ulothrix), or multicellular.The presence of sulphur in the culture medium is considered essential for cell division.It takes place even in the dark with sulphur alone as the source material but under light conditions nitrogen also required in addition.These observations have an important bearing on the concept of the life cycle of Chlorella, which at present is considered to be strictly asexual in character.