Transfer of the red alga Gelidium zollingeri Sonder (Gelidiales) to Yonagunia (Halymeniales) based on morphological and molecular evidence

An examination of the type specimen of Gelidium zollingeri Sonder showed that it was incorrectly placed in Gelidium. To determine the appropriate taxonomic position, we undertook a detailed morphological examination of the holotype (National Herbarium of Victoria, Australia) as well as fresh materials collected from Sempu, the type locality, and a surrounding location Kondang Merak in Malang city, East Jawa, Indonesia. In our collections we found tetrasporangia and carposporophytes on female thalli. The vegetative and reproductive structures clearly placed it in the Halymeniales. Four sequences of rbcL and cox1, two each from Sempu and Kondang Merak, were identical. Our analysis of rbcL sequences showed that G. zollingeri formed a monophyletic clade with the two known Yonagunia species, Y. formosana and Y. tenuifolia. Consequently, we proposed the new combination, Yonagunia zollingeri, based on Gelidium zollingeri. Yonagunia zollingeri was characterized by a cartilaginous, flattened thallus that was subcostate in lower parts, with cystocarpic leaflets that arose on terminal branchlets and round to heart-shaped tetrasporangial leaflets. Yonagunia is now known to occur in Indonesia, Japan (Okinawa), Malaysia, Taiwan, and Vietnam.