Chromosome, morphometric and breeding system studies in the Stylidium caricifolium species complex (Stylidiaceae)

Abstract

Evolutionary relationships among the five species in the Stylidium caricifolium species complex were investigated by chromosome, morphometric and breeding system studies. Marked interspecific chromosome differences were found between all five species and chromosomally polymorphic individuals detected in populations of S. affine, S. caricifolium and S, sp. 2. In addition, chromosomal and morphological intermediates between S. affine and S. caricifolium were found in a region corresponding to an ecological transition zone between the wheat belt and Darling Scarp vegetation systems in southern Western Australia. The origin of these transition-zone forms, although conjectural at this stage, is discussed in the light of information available from chromosome studies.

Morphometric studies demonstrated that S. affine, S. sp. 1 and S. sp. 2 can readily be distinguished from each other and from S. nungarinense and S. caricifolium. The last two species, although not detectably different in the floral characters measured, can be separated on leaf morphology. Breeding system studies suggested that all species with the exception of S. affine and S. caricifolium are effectively isolated from each other reproductively.

The possible significance of chromosome repatterning and eco-geographic patterns in the evolution of the S. caricifolium species complex is discussed.