Chromosome numbers in the genus Mimosa L.: cytotaxonomic and evolutionary implications.

Chromosome numbers were determined for 125 accessions of 92 taxa of Mimosa from all five of Barneby’s (Mem New York Bot Gard 65:1–835, 1991) taxonomic sections. For 69 species, 1 subspecies and 8 varieties, chromosome numbers are presented for the first time, for 6 species and 1 variety previously published data have been confirmed and for 3 species and 2 varieties different numbers were found. Results show that 74% of the accessions were diploid (2n = 2x = 26) and 26% polyploid, these mostly tetraploid (2n = 4x = 52) but with two triploid (2n = 3x = 39). These results double the number of Mimosa species for which the chromosome count is known from less than 10% previously reported to more than 20%, representing an important advance in the cytotaxonomy of this legume genus. These results together with literature data show that ca. 78% of Mimosa species are diploid. Polyploids are present in most of the taxonomic sections and in different lineages across the genus. No particular chromosome number is restricted to a given section or lineage. A possible relation between geography, species distribution, polyploidy and invasiveness was detected, however, further studies based on more accessions, especially from higher latitudes, are required before firm conclusions can be drawn.