Taxonomy of the Genus Halophila Thouars (Hydocharitaceae): A Review

The seagrass genus Halophila Thouars has more than twenty described species and is predominately distributed over a wide geographic range along the tropical and the warm temperate coastlines in the Indo-West Pacific Oceans. A brief history of the Halophila taxonomic development is presented. Based on reproductive and vegetative morphology, the genus is divided into eight sections including three new sections: section Australes, section Stipulaceae and section Decipientes. A rewritten taxonomic description of the type species for the genus Halophila,H. madagascariensis Steudel ex Doty et B.C. Stone, is provided. The lectotype of H. engelmannii Asch. as well as neotypes of H. hawaiiana Doty et B.C. Stone and H. spinulosa (Br.) Asch. are designated. Furthermore, H. ovalis ssp. bullosa, ssp. ramamurthiana and ssp. linearis together with H. balforurii have been recognised as distinct species. Nomenclature, typification, morphological description and botanical illustrations are presented for each taxon. Recent molecular phylogenetic surveys on certain Halophila taxa are also discussed. Field surveys for the deep water Halophila in West Pacific regions are suggested. Morphological studies combined with molecular investigations for the Halophila on the east coast of Africa and the West Indian Ocean are urgently needed and highly recommended.