A review of ploidy in the genus Prosopis (Leguminosae).
The genus Prosopis contains 44 species of trees and shrubs, the majority of which originate in the Americas. Most species are reported to be diploid, with a somatic chromosome number of 2n=28. There are rare reports of polyploidy, although it is thought that these may represent polysomaty in root tissues. However, flow cytometry has recently indicated that P. juliflora is entirely tetraploid with a somatic chromosome number of 2n=56. In order to clarify the situation, an extensive review of ploidy in Prosopis was undertaken, the first of its kind. The ploidy levels of 124 samples of Prosopis from 21 countries, including both the natural and introduced ranges, were analysed using flow cytometry. In addition, a comprehensive literature review was carried out, examining 305 published ploidy values and covering 32 of the 44 species of Prosopis. Flow cytometry analysis suggests that P. juliflora is the only tetraploid species, with a somatic chromosome number of 2n=4x=56, whilst the remainder of the species analysed are diploid with 2n=2x=28, including the first report for P. articulata (2n=28). A critical review of published ploidy values shows that all species of Prosopis are reported to be entirely diploid, except P. glandulosa, P. juliflora, and P. koelziana, for which both diploid and tetraploid values have been recorded.