Taxonomic reappraisal of Dilophus okamurae (Dictyotales, Phaeophyta) from the western Pacific Ocean.

Dilophus okamurae, a common species of brown alga in the warm temperate western Pacific Ocean (Philippines, Taiwan, China, Korea and Japan), is characterized by a typical vegetative morphology that would support its traditional placement in the genus Dilophus. The species has a unilayered cortex, and the medulla is multilayered at least near the margins of the thallus. Sporangia on a two-celled stalk, without an involucrum, however, indicate a close relationship with the recently described genus Rugulopteryx. Molecular phylogenetic analyses, based on three separate loci, large subunit rDNA (LSU), rbcL and psbA confirm the close phylogenetic relationship between D. okamurae and R. radicans, and R. marginatus and R. suhrii. A transfer of D. okamurae to the genus Rugulopteryx is therefore proposed. Contrary to the expected diplobiontic life cycle, typically encountered in Dictyotales, the species exhibits an asexual life cycle consisting of sporophytes only in the populations studied on the east and south coast of Korea. Gametophytes were only obtained by culturing field collected specimens. [ABSTRACT FROM AUTHOR]