A new species of Gibsmithia (Dumontiaceae, Rhodophyta) from mesophotic depths of the Papahanaumokuakea Marine National Monument, Hawai'i, USA

Molecular phylogenetic analyses of Hawaiian members of the red algal family Dumontiaceae were used to clarify the species diversity of Dudresnaya and Gibsmithia from HawaiModified Letter Turned Commai. Although no new species of Dudresnaya were detected in the analyses, D. babbittiana is newly recorded by Lalo, Manawai, and OModified Letter Turned Commaahu; however, this record remains tentative until the type material is sequenced. A new species of Gibsmithia, G. punonomaewa A.R. Sherwood, is described here and reported from the mesophotic depths (79-104 m) of the Papahanaumokuakea Marine National Monument, HawaiModified Letter Turned Commai. This new species differs from all others in the genus based on the following combination of characters: moderate thallus size (up to 11 cm), smooth and terete gelatinous lobes, presence of a stipe (which is often branched), globose carposporangia, and a non-isodiametric shaped cell subtending the tetrasporangia. This new taxon increases the number of Gibsmithia species recorded from HawaiModified Letter Turned Commai to three. Phylogenetically, G. punonomaewa is most closely related to G. dotyi (type locality, Lord Howe Island, Australia) and G. larkumii (type locality, One Tree Island, Queensland, Australia), which are both reportedly widespread in distribution. The relatively dark habitat of the mesophotic in Papahanaumokuakea Marine National Monument contrasts with the surface waters of tropical and subtropical habitats where most Gibsmithia species are found, further highlighting the uniqueness of the species.