DNA analysis identifies 'Solanum' from Litchfield National Park as a lineage of 'S. dioicum'

The uncommon reproductive system of dioecy is somewhat widespread in Solanaceae, being exhibited by members of five genera within this family. These members represent, however, only around 1% of species within the Solanaceae. The highest incidence of dioecy is found in the genus Solanum, where around 15 species have been described as consisting of populations in which individual plants are either “male” (staminate) or “female” (pistillate). Ten of these Solanum species, commonly known as ‘bush tomatoes’, are endemic to the Australian monsoon tropics. During recent fieldwork in the Northern Territory, non-reproductive collections were made of a morphologically distinct population of Solanum (Solanum sp. Litchfield I.D.Cowie 1428) from Litchfield National Park. We generated the first DNA sequences of these exceptional plants, amplifying the ITS (nuclear) and trnK-matK (chloroplast) DNA regions. Phylogenetic analysis comparing molecular data of Solanum sp. Litchfield with previously sequenced relatives infers that the taxon is closely allied to S. dioicum, a widespread species already considered to be morphologically diverse. However, we consider Solanum sp. Litchfield to represent a morphologically and geographically distinct taxon. Although all specimens collected to date lack reproductive features, the phylogenetic placement of Solanum sp. Litchfield infers that the species is likely to be dioecious, thus broadening our understanding of the distribution and circumscription of dioecious lineages of Solanum in Australia.