Summary: Monophylly is exhibited in Monophyllaea and Streptocarpus(Gesneriaceae).Their plant body consists of a single large cotyledon. They never form stems or foliage leaves through their life history, and they produce inflorescences at the base of the cotyledon laminas. Due to such morphological uniqueness, the monophyllous plants(one-leaf plants)have attracted researchers from among many fields, especially evolutionary morphology. Based on recent data from the comparativemorphogenesis and molecular phylogenetic analyses, the evolution of the monophylly in the Gesneriaceae is discussed.