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

The seagrass genus 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 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 Steudel ex Doty et B.C. Stone, is provided. The lectotype of Asch. as well as neotypes of Doty et B.C. Stone and (Br.) Asch. are designated. Furthermore, ssp. , ssp. and ssp. together with have been recognised as distinct species. Nomenclature, typification, morphological description and botanical illustrations are presented for each taxon. Recent molecular phylogenetic surveys on certain taxa are also discussed. Field surveys for the deep water in West Pacific regions are suggested. Morphological studies combined with molecular investigations for the on the east coast of Africa and the West Indian Ocean are urgently needed and highly recommended.