CYTOGENETICS OF SOME SPECIES AND NATURAL HYBRIDS IN PROSOPIS (LEGUMINOSAE)

Cytological results on 12 species and 4 putative hybrids of Prosopis are presented. Of these, 5 species and 4 hybrids have been hitherto unknown cytologically. The following species proved to be diploid (2n = 28) and constitute new chromosome number determinations for the genus: P. algarobilla Griseb., P. hassleri Harms, P. nigra (Griseb.) Hieron., P. patagonica Speg., P. tamarugo Phil. The diploid nature of some races of P. juliflora (Sw.) DC. is established; apparently under this taxon there are also tetraploid populations. The following putative interspecific hybrids showed regular meiosis with formation of 14 bivalents: P. vinalillo Stuck. (P. ruscifolia × P. alba?), P. alba × P. nigra? and P. hassleri × P. ruscifolia?.So far 28 taxa of the genus have been studied cytologically; 27 of these are diploid. The scarcity of polyploidy in the genus (3.5%) might be a consequence of the almost general lack of means of vegetative reproduction and of the absence of chromosome repatterning in primary speciation....