Scenedesmus is is a cosmopolitan green freshwater algae. Because of the colonial symmetry of Scenedesmus, its size/shape differences and abundant cytological features (both LM and EM), it first seemed that individuals could easily be distinguished and classified. Because biologists often examined samples of Scenedesmus taxa at only one point in time, they tacitly assumed that there was stability of form. Are there data confirming stability of form? On the other hand, preserved collections are not useful material to support an alternate hypothesis. The result: hundreds of species and innumerable subspecific taxa were identified and described. In Scenedesmus Phenotypic Plasticity the author presents - Early reports of variability or polymorphism, along with their routine dismissal as supposedly irrelevant observations. - Chapters concerned with geographical distribution, culture techniques, history and the Scenedesmus unicell, indicating the need for the renaissance of the phenotype. The concept of an ordered developmental sequence is developed and discussed. Data from numerous laboratories, whether cytological, morphological, biochemical, ecological or physiological, which lend support to the concept of plasticity in all strains. Numerous supposed taxa are but ecomorphs of rather complex taxa.