Systematic revision of the genus Prionitis (Halymeniales, Rhodophyta) from Taiwan including P. foliagissima sp. nov. and P. imbricata comb. nov

Abstract

Grateloupia imbricata is widely distributed in the northwestern Pacific and northeastern Atlantic Oceans. Recent studies have revealed its close relationship to Prionitis, specifically P. taiwani-borealis from northern Taiwan. In this study, we identified a new species, P. foliagissima sp. nov. based on new G. imbricata-like collections from Taiwan. The female reproductive structures of both G. imbricata (= Prionitis imbricata comb. nov.) and P. foliagissima were examined. We demonstrated that the development of carpogonial branch and auxiliary cell ampullae before and after diploidization were similar to those of P. taiwani-borealis. Namely, in P. foliagissima and P. imbricata, the cells of ampullar filaments after diploidization branched a few times and elongated, together with secondarily produced medullary filaments, forming a cellular cluster surrounding the developing carposporophytes. Prionitis foliagissima can be distinguished from the other species of Prionitis found in Taiwan by its smaller thallus size, strongly twisted branches, as well as densely bullate surface. It was noted that the branched ampullar filaments of the two Prionitis species were weakly developed, which differed from those found in species of Phyllymenia (P. taiwanensis and P. huangiae) from Taiwan, where the cells of auxiliary cell ampullar filaments branched several times to form a dense cellular cluster, and in which most cells remained distinct through maturation of gonimoblasts. Further investigation of the female reproductive structures and postfertilization stages of other lesser-known species of Grateloupia, Prionitis, and Phyllymenia is necessary to understand the generic delineation in the Grateloupia/Prionitis/Phyllymenia complex.