Biologists have studied flowering plants from ancient times. Physiological development of flowers is categorized into four stages viz., floral initiation, floral organization, floral maturation and anthesis. Initiation of flowering is dependent on hormones and environmental conditions. This activates the network of regulatory genes which sequentially signal differentiation of floral primordia into sepals, petals, stamens and carpels. Homeotic mutations have helped to understand the functions of genes involved in flowering. Regulatory genes have been classified into three classes as A, B and C. These genes belong to MADS box transcriptor family. Though ABC model was the first to be proposed new and modified models have also been presented as ABCE and ABCDE models.