Chromosomal change has been important in the evolution of flowering plants. Cytogenetic modifications resulting in dysploid and polyploid alterations of plant genomes have often led to the formation of new species. A genus that represents an excellent example of such changes during its evolutionary history is Melampodium (Asteraceae), occurring primarily in Mexico, Central America, and the southwestern United States. This book is a detailed presentation of the diversity of species in Melampodium, their ecological requirements and phylogenetic relationships, the biogeographic patterns and migrational pathways, chromosomal diversity, and evolutionary origins of species, especially the tetraploids and hexaploids through allopolyploidy. It is an instructive case study of evolution through chromosomal change in a broadly distributed genus of importance in the ecosystems of Mexico and adjacent regions.