Phylogenetic relationships of Coreanomecon (Papaveraceae: Chelidonioideae) inferred from seed morphology and nrITS sequence data

Abstract

The phylogenetic position of the Coreanomecon, a monotypic genus endemic to Korea, has been controversial for a long time. Coreanomecon has variously been placed in its own genus or combined with Hylomecon or Chelidonium. The main purpose of this study was to examine the phylogenetic position of Coreanomecon in relation to genera of the subfamily Chelidonioideae using seed morphology and molecular data. The seed morphology of 10 genera of Chelidonioideae was examined using microtome sections and scanning electron microscopy. The shape and size of exotestal cells varied between genera. The exotestal cells were tangentially elongated in Chelidonium majus, Stylophorum diphyllum and Hylomecon vernalis, whereas the cells were sub‐orbicular and broad in Coreanomecon hylomeconoides. The endotesta was represented by thick palisade‐like cells that contain small rectangular crystals near their outer walls. The mesotesta was totally collapsed in Co. hylomeconoides but wholly or partly persistent in Ch. majus and H. vernalis. The seed surface of Co. hylomeconoides was well ornamented with a unique echinate seed surface, whereas other genera showed plain and reticulate seed surfaces. A phylogenetic analysis of the genera including Coreanomecon was conducted with nuclear ribosomal internal transcribed spacer (nrITS) sequences using genetic distance, maximum parsimony, maximum likelihood and Bayesian inference methods. The results confirm that Co. hylomeconoides is separated from both Hylomecon species and is a sister group to Chelidonium majus and Stylophorum diphyllum with robust bootstrap support. In addition to differences in the absence of cauline leaves and rhizomes, the presence of a hairy stem and leaves, and 12‐pericolpate pollen, seed characters and molecular data strongly support the recognition of Coreanomecon as an independent genus, distinct from Hylomecon and Chelidonium.