Phylogenetic placement of Halophila johnsonii

Halophila johnsonii is an endangered seagrass species that is restricted to the Florida Bay region of Florida, USA. Its taxonomic status has been called into question, in particular, given the close morphological and genetic similarity of H. johnsonii and the widely distributed and morphologically variable H. ovalis, which is largely restricted to the Indo-Pacific region. While a close relationship to H. ovalis is uncontroversial, it remains uncertain whether H. johnsonii represents a distinct lineage or is a recent introduction to the Florida region. Given the conservation status of H. johnsonii, distinguishing these alternatives has important implications for the management of the species and its habitat. Here, we develop molecular data sets for samples of H. johnsonii and H. ovalis including DNA sequences and genome-wide SNPs with the view to resolving the affinities of H. johnsonii with respect to the wider H. ovalis complex.