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 (Citrullus colocynthis (L.) Schrad.), and prickly paddy melon (Cucumis myriocarpus L.), are summer growing invasive weeds found throughout Australia. They infest both natural and agricultural ecosystems and are noxious weeds in some areas of Australia. Camel melon and prickly paddy melon are annuals, while colocynth is a perennial. Camel melon and prickly melon belong to different genera but as they share similar morphology and life history they are often misidentified at the vegetative stage. In this study, a molecular and morphological approach was used to facilitate identification of these melon species. For molecular taxonomic identification, two chloroplast genes matK and ycf6–psbM intergenic spacer and a nuclear gene, G3pdh were used to identify these invasives. The sequences of G3pdh and ycf6–psbM identified camel melon as C. lanatus var. citroides and the colocynth as C. colocynthis, in direct contrast to the current widely published nomenclature (as above). Australian prickly paddy melon sequences at matK revealed it to be Cucumis myriocarpus. For morphological characterisation, populations of each species from selected Australian states were grown in a glass house over a 4-month period in 2011. Each species exhibited distinct leaf lobation, branching of tendrils, floral, fruit and seed attributes, all of which are presented as useful identifying features. This study found that camel melon, colocynth and prickly paddy melon possessed unique morphological characteristics. In addition, each weed was identified to species level using multi locus DNA sequence analysis, demonstrating the utility of this approach for resolving nomenclatural errors and taxonomic mis-identifications.