The genus Catharanthus G. Don, belonging to the family Apocynaceae, comprises a group of small, herbaceous flowering plants known for both their ornamental value and potent medicinal properties, particularly their anticancer activity. The genus consists of nine recognized species, namely, Catharanthus roseus, C. coriaceus, C. lanceus, C. longifolius, C. makayensis, C. ovalis, C. pusillus, C. scitulus, and C. trichophyllus, most of these species are endemic to the island of Madagascar, which is considered as the center of origin and diversity for Catharanthus. From this native region, several species, especially C. roseus (Madagascar periwinkle), have been introduced and cultivated in tropical and subtropical regions worldwide due to their therapeutic significance and adaptability. All species in the genus exhibit relatively small, colourful flowers and are adapted to a wide range of ecological conditions. The present chapter focuses on providing a comprehensive account of the species diversity of medicinal species, geographical distribution, morphological traits, and taxonomic classification of the genus Catharanthus. Additionally, it explores the ecological adaptations that have allowed these species to thrive in various environments. These botanical insights are crucial for understanding the genetic diversity and conservation strategies of the genus, as well as for supporting its continued use in pharmaceutical and horticultural applications.