Variation and Natural Hybridization in the Conostylis aculeata R.Br. Species Group Near Dawesville, Western Australia

Abstract

Variation was studied in allopatric and sympatric populations of Conostylis aculeata R.Br., C. candicans Endl., and C. pauciflora Hopper near Dawesville, on the Swan River Coastal Plain. When in allopatry the three species were found to be morphologically similar but distinguishable by hybrid index analysis. They also showed variable but overlapping habitat preferences. C. paucifora was morphologically intermediate between C. aculeata and a coastal ecotype of C. candicans. Sympatric populations of two pairs of species, C. candicans-C. aculeata and C. pauciflora-C. aculeata, contained intermediate hybrids with slightly reduced pollen fertility relative to the parents. Hybrid populations were confined to ruderal habitats. Ecological factors appeared to be primary in maintaining isolation between the species, since indiscriminate pollination occurred in sympatric populations, and hybrids were abundant and fertile. The taxonomic and evolutionary implications of natural hybridization in the C. aculeata group, including the possibility of a hybrid origin of C. pauciflora, are discussed.