Morphological and molecular analyses consistently support the existence of two species under Hypochaeris achyrophorus (Asteraceae, Cichorieae)

Abstract

The species boundaries in Hypochaeris sect. Seriola (Asteraceae, Cichorieae) are difficult to establish due to the phenotypic similarity between taxa. The main objective of the present study was to characterize the phylogenetic position of the annual Hypochaeris achyrophorus using plastid and nuclear DNA markers, and to determine whether some morphological differences between western and eastern Mediterranean populations are supported by genetic differences. To achieve this, phylogenetic reconstruction, species delimitation analysis and morphometrical analysis of flower characters were carried out. The case provides a fantastic setting to study the evolution of annuality/perenniality and homocarpy/heterocarpy. The results confirm the presence of two distinct taxa within H. achyrophorus: Hypochaeris stuessyi comb. nov., in the westernmost part of the distribution, containing populations with the most ancestral characters, and H. achyrophorus, with biogeographically and morphologically distinct characters, phylogenetically closer to H. laevigata, a perennial species, than to H. stuessyi. Our results indicate that perennial habit and homocarpy are derived characters in the study group that can appear multiple times in evolution, complicating traditional taxonomy. Moreover, when related species with convergent characters are observed, only the use of molecular tools can confirm that subtle morphological differences have distinct evolutionary histories.