Morphological and molecular evidence for two new species of Padina (Dictyotales, Phaeophyceae), P. sulcata and P. calcarea, from the central indo-pacific region

Two new species of Padina - 1. Padina sulcata sp. nov. and 2. P. calcarea sp. nov. - from Malaysia, Indonesia and Palau were described based on morphological and molecular phylogenetic observations. Padina sulcata was a three-layered species characterised by a covering of thick fibrous hairs from the base to the middle of the inferior surface (away from the in-rolled margin) of the thallus; conspicuous equally spaced hairlines that alternated between both frond surfaces; and broad, indusiate oogonial and tetrasporangial sori that occupied nearly the entire fertile zones, and the fertile zones were separated by sterile zones of equal width. Padina calcarea was a two-layered species characterised by a bright yellow inferior surface and a thick calcification on the superior surface (facing to the in-rolled margin), which imparted a strikingly whitish color; inconspicuous hairlines were confined to the inferior surface; and indusiate tetrasporangial sori were just above the hairlines and were found only on the inferior surface. Molecular phylogenetic analyses used chloroplast rbcL and mitochondrial cox3 gene sequences and revealed that the two new species each form strongly supported clades that were genetically distant. Padina calcarea formed an isolated clade that made an early divergence; whereas, P. sulcata showed a sister relationship to P. ryukyuana, indicating a more recent divergence. Padina calcarea was very similar to the Hawaiian P. melemele in gross appearance, particularly in the bright orange to yellow color of the inferior thallus surface and the heavy calcification on the superior surface. However, they were distinguished mainly by the position and arrangement of reproductive sori that were found on the inferior surface and located just above the hairlines in P. calcarea but that were found on the superior surface between the hairlines of the opposite surface in P. melemele. Molecular phylogenetic analyses did not reflect the morphological similarity of the two species because they occupied two distantly related clades.