Evolution and Natural History of the Cotton Genus

We present an overview of the evolution and diversity in Gossypium (the cotton genus). This framework facilitates insight into fundamental aspects of plant biology, provides the necessary underpinnings for effective utilization of cotton genetic resources, and guides exploration of the genomic basis of morphological diversity in the genus. More than 50 species of Gossypium are distributed in arid to semi-arid regions of the tropics and subtropics. Included are four species that independently have been domesticated for their fiber, two each in Africa-Asia and the Americas. Gossypium species exhibit extraordinary morphological variation, ranging from trailing herbaceous perennials to ∼15 m trees with a diverse array of reproductive and vegetative characteristics. A parallel level of cytogenetic and genomic diversity has arisen during the global radiation of the genus, leading to the evolution of eight groups of diploid (n = 13) species (genome groups A through G, and K). Data implicate an origin for Gossypium about 5–10 million years ago and a rapid early diversification of the major genome groups. Allopolyploid cottons appear to have arisen within the last 1–2 million years, as a consequence of trans-oceanic dispersal of an A-genome taxon to the New World followed by hybridization with an indigenous D-genome diploid. Subsequent to formation, allopolyploids radiated into three modern lineages, two of which contain the commercially important species G. hirsutum and G. barbadense.