Cytoevolution in the genus Calotis R. Br. (Compositae: Astereae)

Abstract

Calotis is a genus of about 26 species and subspecies, which are chiefly encountered in the arid and semiarid regions of eastern Australia. A cytological analysis of 21 species is reported here.

There are two significant trends in the cytoevolution of the genus. Chromosome number reduction from the base number of n = 8 down to n = 4 is found mainly in arid zone annuals; some arid zone perennials are n = 7. Polyploidy occurs in two-thirds of the species, and it is as frequent in low-number annuals as in higher-number perennials. B chromosomes have been found only rarely.

Forms of asexual reproduction occur in the genus, and at least one agamic complex involving polyploidy has occurred. Other species appear to be obligate outbreeders.