Molecular phylogeny and morphometric analyses in the genus Cousinia Cass. (Family Asteraceae), sections Cynaroideae Bunge and Platyacanthae Rech. f.

Abstract

Taxonomy and molecular phylogeny of the genus Cousinia are complicated and unresolved mainly because of disagreement between morphological and molecular phylogenetic studies. The genus Cousinia has approximately 700 species, which makes it one of the most varied genera found in central and southwest Asia. Section Cynaroideae, containing 89 species, is considered the largest section of the genus. Identification and delineation as well as classifying the section and the species’ relationships within the genus Cousinia generally remain debatable. Therefore, the present study aims to: 1) identify and delineate the species within the two sections Cynaroideae and Platyacanthae; 2) study the species relationships based on both morphological and molecular features (Internal Transcribed Spacer (ITS) marker); 3) study the sectional delimitation and its monophyly; and 4) estimate the divergence time of the studied sections. To this end, 50 Cousinia species occurring in Iran were investigated for the first time. A maximum parsimony tree of the morphological features separated the species of the two sections from each other. However, the ITS-based phylogenetic tree did not delimit the two studied sections. The relationships among the studied Cousinia species in the genetic trees were generally not congruent with the obtained morphological tree. The divergence time of the studied species within the Cynaroideae and Platyacanthae sections determined using Bayesian Evolutionary Analysis Sampling Trees (BEAST) was estimated to be around 3.5 million years ago (Mya).