Chlamydomonas reinhardtii alga. Chlamydomonas reinhardtii is a common green unicellular alga. For more than 50 years it has been a favored model organism for a wide range of different fields in modern biology. Here I discuss both the history of its use in the study of photosynthesis and the most recent results in the study of cell cycle regulation, polycystic kidney disease and hydrogen production.