Taxonomy of the genus Padina (Dictyotales, Phaeophyceae) based on morphological and molecular evidences, with key to species identification

Taxonomic study of the brown algal genus Padina (Dictyotales, Phaeophyceae) mainly
from Southeast Asian countries, Japan, Hawaii, Australia and Taiwan as well as the Mediterranean Sea was conducted based on morphology and molecular phylogenetic analyses using chloroplast encoded large subunit RuBisCo (rbcL) gene sequences. Detailed descriptions of each species found in this study as well as key to species identifi cation are described. Several morphological characters, such as number of cell layers composing the thallus, presence or absence and degree of calcifi cation, presence or absence of small groups of rhizoid-like hairs, presence or absence of Vaughaniella stage, structure, position and arrangement of hairlines and reproductive sori, reproductive system (monoecism or dioecism), and presence or absence of indusium over/surrounding reproductive sori, are considered to be reliable morphological characters for species delineation. Variation of the presence (female gametophyte) and absence (male gametophyte and tetrasporophyte) of indusium was recognized in P. australis, indicating a necessary of a careful examination on this character. Molecular phylogenetic analyses using rbcL gene sequences revealed that multi-layered species formed monophyletic, whereas 2-layered and 2/4-layered species were paraphyletic. Only a single species with 2/3-layered thallus was included in the molecular analyses.