Taxonomy and species diversity of Padina (Dictyotales, Phaeophyceae) from the Indo-Pacific with the description of two new species

ABSTRACT Taxonomy, species diversity, and geographical distribution of the marine brown algal genus Padina (Dictyotales, Phaeophyceae) from tropical South-East Asian waters were investigated through a combination of morphological and molecular analyses. The study presents a new schematic diagram showing a suite of morphological characters including thallus hairline structures that are useful for species delineation in the genus. This study also revealed two new species from Myanmar, P. gracilis sp. nov. and P. lata sp. nov. based on molecular and morphological data. P. gracilis is characterised by a 2-layered thallus, thin hairlines on both surfaces of the thallus at equal distances, non-indusiate reproductive sori distally very close to the hairlines on the inferior surface, and the presence of Vaughaniella stage. P. lata is characterized by a 2–4-layered tiny thallus, broad hairlines located only on the inferior thallus surface, non-indusiate reproductive sori abutting the hairlines on the inferior surface and irregularly spreading on the superior surface, and the presence of Vaughaniella stage. This study also revealed new distributional records for four Padina species: P. okinawaensis from Myanmar and P. fasciata, P. ryukyuana and P. terricolor from the Philippines. These findings point to elevated species diversity in central Indo-Pacific waters. This study confirmed that most of the Padina species in the Pacific regions are showing overlapping distribution across the regions, in contrast to species from the Indian Ocean, which tend to be confined to specific localities.