Characterization of <i>Martensia</i> (Delesseriaceae; Rhodophyta) from shallow and mesophotic habitats in the Hawaiian Islands: description of four new species

Fifty-six specimens of the red algal genus <i>Martensia</i> from the Main and Northwestern Hawaiian Islands, representing both shallow (36 specimens from 0–20 m depth) and mesophotic habitats (20 specimens from 62–93 m depth), were collected and characterized using morphological and molecular analyses. Phylogenetic analyses of the <i>rbc</i>L gene resolved five distinct clades of <i>Martensia</i> from the Hawaiian Islands, of which none could be attributed to the two previously used taxonomic names for this flora (<i>M. fragilis</i> Harvey and <i>M. flabelliformis</i> Harvey <i>ex</i> J.Agardh). Analyses of the COI barcoding region were consistent with <i>rbc</i>L trends, although fewer specimens amplified and sequenced for this marker. Four <i>rbc</i>L clades (lineages 1–4) were distinct from each other and from other described species of <i>Martensia</i> based on both phylogenetic position and morphological characters, and are here described as new species: <i>Martensia abbottiae</i> A.R.Sherwood &amp; S.-M. Lin sp. nov., <i>Martensia hawaiiensis</i> A.R.Sherwood &amp; S.-M. Lin sp. nov., <i>Martensia tsudae</i> A.R.Sherwood &amp; S.-M. Lin sp. nov., and <i>Martensia lauhiekoeloa</i> A.R.Sherwood &amp; S.-M. Lin sp. nov. Lineage 5 is attributable to <i>M. albida</i> Y.Lee. All five species in the Hawaiian flora occur in mesophotic habitats, while <i>M. hawaiiensis, M. tsudae</i>, and <i>M. albida</i> also inhabit shallow waters of the Main Hawaiian Islands. This study provides additional support for the degree of uncharacterized biodiversity from mesophotic depths in the Hawaiian Archipelago.