Chromosome evolution within theOrnithogalum tenuifolium complex (Hyacinthaceae), with special emphasis on the evolution of bimodal karyotypes

Hypotheses on the evolution of the karyotypes of 8 chromosome races (2n = 4, 6, 8, 10, 12, 16-two forms, 26) within theOrnithogalum tenuifolium complex are discussed. Four of the karyotypes are strictly bimodal: 2n = 8 (6 long and two short chromosomes), 2n = 10 (6 long and 4 short chromosomes), 2n = 12 (6 long and 6 short chromosomes) and 2n = 16 (12 long and 4 short chromosomes). The hypotheses are tested by means of measurements of nuclear DNA content, studies of meiosis and pollen fertility of hybrids, and comparisons of karyotype morphology. The results indicate that the E. African 2n = 12 chromosome race is the most primitive and has given rise to the other chromosome races. The 2n = 6 race is found to have a significantly higher fitness than the 2n = 12 race.