New records of Myelophycus cavus (Scytosiphonaceae, Phaeophyceae) in Korea and the taxonomic position of the genus on the basis of a plastid DNA phylogeny

Myelophycus is a brown algal genus that includes only two species worldwide: M. cavus and M. simplex. M. simplex occurs commonly in the Northwest Pacific and M. cavus was reported only in Japan. Here we report the occurrence of M. cavus in Korea for the first time. The species Occurred in the upper intertidal on the west and south coast. Thalli were twisted and hollow, having small plurilocular zoidangia (c. 90 mum long) and unilocular sporangia (c. 50 mum long). Plastid DNA (rbcL and Rubisco spacer) sequences were determined in Myelophycus and compared with homologous positions of newly sequenced putative relatives (Analipus japonicus, Asperococcus fistulosus, Chordaria flagelliformis, and Punctaria latifolia) and with published sequences of other brown algae. Extensive interspecific divergences of the rbcL and Rubisco spacer were found in Myelophycus. Supporting the recent classification of five families in the Ectocarpales, our data of plastid DNA sequences also show that Mylelophycus consistently formed a monophyletic clade with a maximum support together with the Scytosiphonaceae. Within this lineage, Myelophycus clustered with taxa having only unilocular sporangia on their sporophytes, while internal branches were less resolved. Based on the plastid DNA sequences and synapomorphic characters such as parenchymatous tissue, a single plastid with a pyrenoid per cell, and hormosirene, we propose to place Myelophycus (formerly classified in the Asperococcaceae or in the Punctariaceae or in the Chordariaceae sensu lato) in the Scytosiphonaceae and emend the circumscription of that family to include also isomorphic life histories in addition to those with heteromorphic patterns.