1. Introduction Constantine John Alexopoulos (1907–1986) was a prominent Greek-American mycologist whose textbook, Introductory Mycology , became a standard reference for university-level mycology. His classification system, primarily presented in the second and third editions, was a landmark effort to organize the fungi based on a combination of morphological, developmental (ontogenetic), and reproductive characteristics. While largely superseded by molecular phylogenetics, the Alexopoulos system remains historically significant and is still used as a practical framework for teaching fungal diversity.