The Reproductive Strategies of Scandent Groundsels Senecio Angulatus and Senecio Mikanioides (Asteraceae, Senecioneae)

Abstract

Senecio angulatus and Senecio mikanioides originated from South Africa and are predominant weeds in the Wellington area. Research found that no seed was produced in Wellington populations of either species. Artificial hand pollination experiments suggest that a lack of pollinators is not the reason for limited seed production. Viewing artificially pollinated stigmata stained with aniline blue under a UV microscope showed that a low number of pollen grains adhered to the stigmatic surface. Callose was present in the few pollen tubes that did adhere to the surface, indicating the presence of a sporophytic self-incompatibility mechanism. A vegetative experiment showed that cuttings of various ages and lengths and treatments including those grown horizontally and buried under sand and leaves had the ability to establish in both species. This supports the hypothesis that populations of S. angulatus and S. mikanioides are both comprised of a single genotype, or at least are fixed for a single S allele so that seed is unable to be produced. Therefore the predominant mode of dispersal of S. angulatus and S. mikanioides in the Wellington region is considered to be by vegetative reproduction.