Biosystematic studies in the Stylidium crassifolium species complex (Stylidiaceae)

Abstract

Stylidium elongatum Benth. (n = 13, 26) and Stylidium crassifolium R. Br. (n = 14, 28) have been restored to specific status and a morphologically intermediate species, Stylidium confluens sp. nov. (n = 14), is described. Polyploid entities in the complex have not been given taxonomic ranks although the tetraploid form of elongatum may be considered worthy of subspecific rank, as it is ecologically distinct and contiguously allopatric to its progenitor and to confluens, forming a buffer between these two diploid entities. Tetraploid populations in crassifolium occur within the distributional range of the diploid. All three species carry recessive lethal gene arrays which eliminate the products of self-pollination with great efficiency and result in crosses between close populations yielding seed more effectively than crosses within populations. There is evidence that interpopulational coadaptation may break down with increasing distance between populations. Polyploidy in crassifolium is probably a conservative response in the genetic system of a species where concentrations of lethal genes in small diploid populations became disadvantageous.