Defining conservation units in a species complex with genomic-taxonomic discordance: a case study of Conospermum caeruleum (Proteaceae)

Morphologically variable species complexes can present significant challenges to conservation when taxonomic boundaries, and therefore conservation units, are ambiguous. In such cases, the definition of Evolutionarily Significant Units (ESUs) based on high-resolution genomic data can be an effective method to clarify genetic divergence and inform conservation actions. Here, we employ a population genomic approach using SNP data to delineate conservation units in a morphologically ambiguous plant species complex ( Conospermum caeruleum ; Proteaceae) from a global biodiversity hotspot. Over 200 individuals representing five subspecies and three informal morphological forms were sampled across a wide geographic range. Phylogenomic (ML tree and SplitsTree network) and population genomic (STRUCTURE, PCoA, F ST ) analyses resolved three divergent genetic groups that were incongruent with the current taxonomy, but consistent with geographic distribution. One ESU was comprised of three genetic subgroups, and these can be considered Management Units (MUs) to conserve population genetic structure and diversity. These MUs were surprisingly incongruent with the current subspecies-level taxonomy, but one MU was consistent with a recently documented morphological form, and all were consistent with ecogeographic distribution. We recommend a full taxonomic revision of the Conospermum genus based on a phylogenomic approach to assess any wider incongruence with morphology, and that conservation strategies should be informed by genetic data. Our study exemplifies the application of genomics to the conservation of a morphologically ambiguous species complex, enabling and enhancing the practical conservation of appropriate units of biodiversity.