Date of Thesis



Botanists have recognized problematic species boundaries among the functionally dioecious spiny solanums of northern Australia for decades. Of the ca. 15 species in this group, the Northern Territory sandstone endemic Solanum asymmetriphyllum stood out as one of the most morphologically distinct until its sister species, S. sejunctum, was described in 2006. While molecular work supports that these two taxa are likely sister species, our work revealed that interspecific crosses lead to fruit and seed set, and a high germination rate for an F1 and F2 hybrid generation. The goal of this study was to investigate the F1 hybrids and make morphological and genetic comparisons of them to the two parent species. Morphometric analyses included vegetative and reproductive characteristics and found an equal number of characters favoring both parental species, exhibiting an intermediate hybrid morphology, and possessing a unique hybrid effect where hybrid morphology was distinctive. Molecular analyses included chromosomal ploidy level determination and a species-determining restriction enzyme digestion pattern assay of the sporopollenin precursor gene CYP703. Chromosomal cell spreads indicated that both species and all hybrids maintain the same chromosome number (2n=24) and that allopolyploidy had not occurred. The CYP703 species-determining assay determined that the two species are distinct and the hybrids have a mixed digestion gel pattern. A recently collected herbarium specimen of a putative wild hybrid (labeled as S. asymmetriphyllum, but resembling an intermediate form with S. sejunctum) suggests that natural hybrids occur or a new species should be recognized. All of these data better clarify the evolutionarily close relationship between S. asymmetriphyllum and S. sejunctum and solidify their position as distinct species. The ability for the two species to form hybrid offspring into the F1 and F2 generations suggests that they are recently diverged; and some outcomes of the study infer that the speciation of S. sejunctum may have occurred as a result of a single population becoming geographically isolated during periods of climate change via vicariance or long distance dispersal. Providing support for the distinction of species helps determine the necessity for any conservation efforts to maintain stable population sizes--especially for S. sejunctum, which is isolated on a single sandstone monolith.


botany, hybridization, plant morphology, genetics, australia, solanum, solanaceae

Access Type

Masters Thesis (Bucknell Access Only)

Degree Type

Master of Science



First Advisor

Christopher Martine