Two new species of Padina (Dictyotales, Phaeophyceae) from southern Japan, P. ogasawaraensis sp. nov. and P. reniformis sp. nov., based on morphology and molecular markers

Two new bistratose species of the brown algal genus Padina, P. ogasawaraensis sp. nov. and P. reniformis, sp. nov., were discovered from Ogasawara and Okinawa Islands, and Kagoshima, Japan, respectively, and characterised based on a combination of morphological and molecular analyses. Padina ogasawaraensis is characterised by a semicircular or circular yellowish-brown thallus with light to heavy calcification except at the hairlines and presence of hairlines on both surfaces in an alternating sequence. These can be seen as a broad-depressed line with a remnant of a thin red hairline at its center on the inferior surface and as a narrow or sometimes rudimentary line on the superior surface. Indusiate reproductive sori are located distally adjacent to the hairlines on the inferior surface, partially to deeply embedded in the epidermis layer. Padina reniformis is characterised by a semicircular or kidney-shaped greenish brown thallus with light to moderate calcification on both surfaces of the thallus. Hairlines are present only on one (inferior) surface and are narrow, not depressed. Indusiate tetrasporangial sori are arranged in two to three rows between the hairlines on the inferior surface and situated on the thallus surface. Molecular phylogenetic analyses using rbcL and cox3 DNA sequences placed them in distantly related clades. Padina ogasawaraensis showed a sister relationship to P. calcarea; whereas, P. reniformis was sister to P. fasciata.