CHROMOSOME CYTOLOGY OF IRIDACEAE - PATTERNS OF VARIATION, DETERMINATION OF ANCESTRAL BASE NUMBERS, AND MODES OF KARYOTYPE CHANGE

Against a background of 100 original counts for 95 species in 34 gener a of Iridaceae, we review chromosome information for the entire family . Counts are now available for some 1008 of the estimated 1750 species of Iridaceae, and all but 5 of ca. 78 genera are known from at least one count. me suggest ancestral base numbers far all genera known cyto logically and outline patterns of cytological variation within the sub families and tribes currently recognized. Polyploidy was evidently imp ortant in the early diversification of Iridaceae, and many genera have base numbers higher than I = 10. Neopolyploidy is important in Northe rn Hemisphere genera, especially Iris and Crocus, but has an unusually low frequency in Africa, the center of diversity for the family. Chan ges in basic number, frequent in a few genera, are evidently tile resu lt of dysploid reduction. In all but a few possible examples, correlat ed morphological specialization suggests that dysploid reduction is in volved in stepwise change in base number. Major dysploid series are re stricted to a felv genera, including Romulea, the related Crocus, as w ell as Gladiolus and Lapeirousia (ail Ixioideae), and Iris, Moraea, an d Sisyrinchium (Iridoideae). All other genera have a single base numbe r or limited variation evident in only one or two species. Patterns of chromosomal variation are particularly complex in Iris and Crocus and await detailed elucidation. More counts are needed in the Australian Patersonia, the South American-Australasian Orthrosanthus, and the neo tropical tribe Mariceae, for all of which ancestral base number remain s uncertain and patterns of cytological variation appear complex.