Mitella amamiana sp. nov., the First Discovery of the Genus Mitella (Saxifragaceae) in the Central Ryukyus

Abstract

In this report, I describe the morphological characteristics, evolutionary relationships, and taxonomy of a newly discovered perennial Mitella amamiana sp. nov. (section Asimitellaria; Saxifragaceae) on Amami-Oshima Island in the central Ryukyus. The discovery is noteworthy because the genus Mitella has been considered absent from the central and southern Ryukyus. Using phylogenetic analyses based on nuclear ribosomal DNA (ETS and ITS) and the two copies of nuclear Granule-bound starch synthase genes (GBSSI-A1 and GBSSI-A2), M. amamiana appears to have a sister relationship with M. doiana Ohwi, which is endemic to Yakushima island in the northern Ryukyus. Mitella amamiana is morphologically similar to M. doiana but clearly differs in the occasional presence of petals and the size of the leaves. Considering that plants of Mitella have low dispersability, the present discovery provides a valuable opportunity to characterize biogeographic associations across the Tokara gap, an ancient and continuous land break between the central and northern Ryukyus.