Population genetic structure and range limits of Prostanthera cineolifera (Lamiaceae), a vulnerable shrub with a patchy distribution

Integrating molecular data is essential for clarifying the distributions and genetic structures of species that have histories of misidentification and misapplication of names. There has been confusion about the species limits of the Vulnerable Prostanthera cineolifera with respect to morphologically similar specimens in the Hunter Valley, New South Wales, Australia and morphologically dissimilar specimens in the Lower Hawkesbury Valley, New South Wales, and from north-eastern New South Wales. To test the species limits of P. cineolifera, and related taxa, specimens were collected from across the range and augmented with herbarium specimens. We used morphometric analysis of 18 morphological characters across 51 samples. Using the DArTseq reduced representation sequencing platform, 4010 single-nucleotide polymorphisms (SNPs) across 110 individuals were recovered for molecular analysis. Both morphological and molecular analyses produced three concordant clusters (A) P. cineolifera, (B) a group sharing similarities with P. sp. Hawkesbury (B.J.Conn 2591), and (C) a group allied with P. lanceolata and P. ovalifolia. These results indicate that the specimens form north-eastern New South Wales are more likely to be P. lanceolata, not P. cineolifera, and that specimens from the Lower Hawkesbury are of an undescribed species with the phrase name P. sp. Hawkesbury (B.J.Conn 2591). Within P. cineolifera there was pronounced genetic differentiation among populations. Little evidence of inbreeding was observed, but the newly recognised, more isolated populations had the lowest genetic diversity. This study provides new information about the range of the species and its genetic structure that informs the conservation priorities for this species.