Tangled evolutionary history: genetically divergent taxa and hybrids characterise lantana invasions in Australia

This study investigated population genomic diversity and structure in the taxonomically complicated and highly invasive Lantana camara L. (Verbenaceae) species complex in Australia. We considered taxonomy, spatial distribution and patterns of morphological and genetic variation in populations across the main invaded area (i.e., coastal and subcoastal eastern Australia across 22° latitude), and reconstructed their relationships with native-range plants sampled from the Americas. We used DArTseq to generate genome-wide single nucleotide polymorphism (SNP) data for > 600 individuals and analysed data from > 20,000 SNPs to identify genetic structure, and test the extent to which it corresponded with taxonomic descriptions and morphotype concepts used in current lantana biological control programmes. A subset of individuals was also evaluated for ploidy variation using flow cytometry. We used MaxEnt to predict suitable habitat for invasive lantana in Australia, and compared predictions with current distribution patterns, together with variation in morphology and biological control agent susceptibility. Invasive lantana in Australia was not clearly related to any native-range Lantana species. Instead, it was characterised as a mosaic of several distinct and divergent genetic lineages, from common and widespread to rare and localised, interspersed with occasional inter-lineage hybrids. This complexity explains why the taxonomy of invasive lantana has been (and will continue to be) challenging. Nevertheless, the main genetic lineages identified here were in agreement with published taxonomic concepts (varieties). Two of these varieties (Common Pink and Common Pink-Edged Red) were found to be dominant, widespread and occupying the full extent of their predicted suitable habitat in Australia. Failing to distinguish different taxa within invasive lantana may affect the success of biological control; taxonomic revision is thus needed to comprehensively define invasive taxa and provide broadly-applicable tools to identify them accurately.