Cytogeography of the genus Eremophila

Abstract

Polyploidy is of relatively frequent occurrence in Eremophila (x = 18). In 27 species examined karyologically from four or more localities, 13 were uniformly diploid, one was uniformly tetraploid, and 13 showed infraspecific polyploidy, diploid and/or tetraploid and/or hexaploid races being recorded. In most cases the chromosome races within a species have a pattern of geographical replacement. It is suggested that the formation of polyploid biotypes may lead to geographical expansion into new territory. Polyploidy may be effective in fixing adaptive recombinants near the margins of the diploid area, or may have direct adaptive effects on cell physiology. The ancient land surfaces of Western Australia appear to be a reservoir for relic diploid populations. In a few cases closely related entities which occur sympatrically have been found to be at different ploidy levels in the area of overlap. It is suggested that polyploidy in Eremophila has also facilitated the establishment of genetic isolation between differentiating biotypes.