Phylogenetic relationships of the rare Korean monotypic endemic genus Pentactina Nakai in the tribe Spiraeeae (Rosaceae) based on molecular data

Abstract

The phylogenetic position of Pentactina Nakai, one of only six endemic genera in the Korean peninsula, has been elusive and difficult to determine due to inaccessibility of plant materials. In this paper, we were able to obtain material from the one and only living collection of Pentactina outside of its native range in North Korea and determined its phylogenetic relationship relative to the other genera within the tribe Spiraeeae (Rosaceae). This paper presents the first molecular phylogeny of the genus Pentactina using both nuclear ribosomal ITS regions as well as chloroplast DNA trnL-trnF intergenic spacers to conduct phylogenetic analyses (maximum parsimony and maximum likelihood) of the Spiraeeae. The ITS and combined data set trees suggest that Pentactina shares its most recent common ancestor with Petrophyton, a small western North American genus, while cpDNA suggests close relationships to Kelseya, Sibiraea, and Petrophyton. Therefore, based on the present molecular sequence data, we suggest that the rare Korean monotypic endemic genus Pentactina possibly has a close relationship with the small western North American genus Petrophyton, although receiving a weak support. In addition, our current study suggests that Pentactina is not part of the large genus Spiraea as previously hypothesized by Hutchinson. Pentactina possess combinations of several morphological features within the Spiraeeae such as an erect shrub habit, simple serrate leaves, and raceme inflorescences, and recognition as a distinct endemic genus in Korea is warranted.