Evolutionary history of the genus. As
Gossypium diversified and colonized arid regions
of the globe it underwent extensive chromosomal evolution. Presently, eight
diploid genome groups (A through G,
plus K) are recognized among the 50 species. Relationships within and among the various
genome groups have been addressed in detail.
Genome groups largely correspond to monophyletic lineages.
This information has been embodied in our synthesis of relationships and of
genome evolution, which reveals four major lineages of
diploid species corresponding to three continents.
Phylogenetic framework and genome size variation.
Gossypium contains 45
diploid (n = 13) and five
allopolyploid (n = 26) species, the latter with two
genomes, A and D, from species in different hemispheres.
A- and D-genome groups diverged ~ 5-10 MYA.
Allopolyploid cottons originated following
trans-oceanic dispersal of an A-genome progenitor to the New World. Arrows indicate
taxa representing the best living models of the species
involved in allopolyploid formation. Allopolyploids diversified during
the Pleistocene into three lineages, of which two include the commercially
important species, G. hirsutum (upland cotton) and G. barbadense (Pima cotton), each domesticated
within the last 4000-7000 years.