Identification of the invasive weeds, camel melon, prickly paddy melon and colocynth in Australia: A morphological and molecular approach

Camel melon (Citrullus lanatus (Thunb.)Matsum. & Nakai var. lanatus), colocynth (Citrulluscolocynthis (L.) Schrad.), and prickly paddy melon(Cucumis myriocarpus L.), are summer growinginvasive weeds found throughout Australia. Theyinfest both natural and agricultural ecosystems andare noxious weeds in some areas of Australia. Camelmelon and prickly paddy melon are annuals, whilecolocynth is a perennial. Camel melon and pricklymelon belong to different genera but as they sharesimilar morphology and life history they are oftenmisidentified at the vegetative stage. In this study, amolecular and morphological approach was used tofacilitate identification of these melon species. Formolecular taxonomic identification, two chloroplastgenes matK and ycf6'psbM intergenic spacer anda nuclear gene, G3pdh were used to identify theseinvasives. The sequences of G3pdh and ycf6'psbMidentified camel melon as C. lanatus var. citroides andthe colocynth as C. colocynthis, in direct contrast tothe current widely published nomenclature (as above).Australian prickly paddy melon sequences at matK revealedit to be Cucumis myriocarpus. For morphologicalcharacterisation, populations of each species fromselected Australian states were grown in a glass houseover a 4-month period in 2011. Each species exhibiteddistinct leaf lobation, branching of tendrils, floral, fruitand seed attributes, all of which are presented as usefulidentifying features. This study found that camelmelon, colocynth and prickly paddy melon possessedunique morphological characteristics. In addition, eachweed was identified to species level using multi locusDNA sequence analysis, demonstrating the utility ofthis approach for resolving nomenclatural errors andtaxonomic mis-identifications.