Central American and Mexican region. North American region. Species without an identified region. Index of botanical names. For important crops, regions of diversity of related wild species are also presented.
Wild species are often useful sources of genes to improve the value of crops.
Species cultivated primarily as ornamentals and timber crops, and useful lower plant species are not included. Taxa are arranged alphabetically first by family, secondly by genus and thirdly by species within genera. Somatic chromosome numbers and genome formulae are presented where known. Most of the chromosome numbers are derived from Bolkhovskikh et al. Where the chromosome number could not be traced, a space has been left open.