First chromosome number determinations in south-eastern South American species of Lupinus L. (Leguminosae)

Chromosome numbers are presented for the first time for 30 accessions of nine south-eastern South American Lupinus species. Chromosome numbers of 2n = 32 and 34 were found for L. bracteolaris (three out of five accessions with 2n = 32) and L. linearis (two out of three accessions with 2n = 32), and of 2n = 36 for L. gibertianus, L. lanatus, L. magnistipulatus, L. multiflorus, L. rubriflorus, L. reitzii and L. uleanus. All the South American species examined have relatively low chromosome numbers when compared with most of the Old World and North American species. Our results, where 2n = 36 is the rule, are in sharp contrast to the data for North American Lupinus species and reveal the following: (1) low chromosome numbers are the rule, at least in the southern part of eastern South America; (2) cytologically, the eastern South American species form a group distinct from the North American taxa; (3) high levels of polyploidy have not played as important a role in evolution and speciation in eastern South America as in North America; (4) the predominance of low chromosome numbers in eastern South American species and the existence of similar numbers in two of the six rough-seeded Old World species support the hypothesis that in the evolution of the genus the eastern South American species branched off first, followed by the rough-seeded group. (C) 2002 The Linnean Society of London.