Molecular phylogeny and taxonomy of the Hydrangea serrata complex (Hydrangeaceae) in western Japan, including a new subspecies of H. acuminata from Yakushima

Abstract

According to the contemporary classification of Hydrangea native to Japan, H. serrata is a polymorphic species including six varieties. We discovered a plant identified as H. serrata, but morphologically distinct from previously known varieties, in Yakushima island where approximately 50 endemic species are known. To determine the relationship of this plant with previously known varieties, we examined morphology and constructed a highly resolved phylogeny of H. serrata and its relatives using three chloroplast genomic regions, rbcL, trnL intron, psbA-trnH, and two nuclear genomic regions, ITS1 and ITS2, and Multiplex ISSR genotyping by sequencing (MIG-seq). Based on these morphological and phylogenetic observations, we describe Hydrangea acuminata subsp. yakushimensissubsp. nov. as a newly discovered lineage in Yakushima, Japan and propose Hydrangea minamitaniistat. nov. and Hydrangea acuminata subsp. australisstat. nov. which were previously treated as varieties of H. serrata.