QUANTITATIVE CYTOGENETIC ANALYSES OF AUTOPLOID AND ALLOPLOID TAXA IN THE HELIANTHUS-CILIARIS GROUP (COMPOSITAE)

Diploidy, tetraploidy, and hexaploidy occur in the Helianthus ciliaris complex. Quantitative cytogenetic analysis shows that both auto- and allotetraploids and auto-allohexaploids occur in H. ciliaris. There is evidence for pairing control mutations in and among populations of bo th cytotypes, and this should be expected with increasing age in any n ormal diploid or autopolyploid population. The autotetraploid populati ons contain the model genomes AAAA and the hexaploid AAAABB. The B gen ome may have been derived from diploid H. laciniatus whose range overl aps the tetraploid cytotype in Texas and New Mexico and may have provi ded the drought tolerance necessary for the hexaploid H. ciliaris cyto type to become a successful weed in more arid regions of its distribut ion.