Monoraphidium, a genus of green algae in the family Selenastraceae, is commonly found floating freely or attached to surfaces in freshwater and soil environments. It is widespread globally and a prevalent type of phytoplankton in freshwater habitats. Monoraphidium cells are single-celled and range from 2 to 182 micrometers in length and 1 to 8 micrometers in width. They exhibit various shapes including straight, lunate, sigmoid, or helical. Each cell contains a single nucleus, a parietal chloroplast, and may have a pyrenoid without a starch sheath or lack a pyrenoid altogether. Reproduction occurs through asexual means by autospores. Monoraphidium is distinguished from its closely related genus Ankistrodesmus primarily by its typical unicellular nature. Certain species like Monoraphidium neglectum show potential as valuable candidates for commercial biofuel production.