CHROMOSOME VARIATION IN STYLIDIUM-CROSSOCEPHALUM (ANGIOSPERMAE, STYLIDIACEAE) AND THE DYNAMIC CO-ADAPTATION OF ITS LETHAL SYSTEM

Extensive chromosome repatterning was demonstrated in Stylidium crossocephalum F. Muell by means of karyotype analysis of a sample of 191 native plants taken from 69 collection sites throughout the species range between Yanchep and Geraldton on the coastal sand plain north of Perth in Western Australia. Both polymorphic and polytypic variation occurred. Of the 42 haploid genomic combinations of chromosomes defined in this study, no less than 26 were found as heterozygotes only and were of localized occurrence. 16 stable genomes, occurring as homozygotes, generally had more extensive but polytypic distributions. Although pollen fertility in native plants was always found to be greater than 40%, and usually greater than 90%, synthetic crosses proved to be totally or almost completely pollen sterile. This is explained on the hypothesis that chromosome repatterning in this species is associated with the generation and modulation of recessive zygotic lethal systems which exist in locally coadapted combinations. These eliminate the products of self fertilization while permitting the relatively free development of cross pollination products in natural populations. © 1979 Springer-Verlag.