Species delimitation in the genus Cousinia Cass. (Family Asteraceae), sections Cynaroideae Bunge and Platyacanthae Rech. f.: morphometry and molecular analysis

Abstract

The genus Cousinia Cass. of the tribe Cardueae with about 700 species is one of the most diverse genera in Central and SW Asia. Section Cynaroides Bunge with 89 species is the largest section of the genus.Due to controversy in the number of Cousinia species and their delineation, the first step in studying the genus is to identify and delimit presumed species. Species delimitation is usually difficult in the species with overlaps in their morphological features. We therefore, used a combination of morphological and molecular markers (ISSRs) to carry out delimitation in 204 taxa of 68 Cousinia species sections Cynaroideae Bunge and Platyacanthae Rech. f.. The species delineation based on morphometry and ISSR data were done by UPGMA clustering. The samples of each species were placed close to each other and formed a single sub-cluster, separated from the other studied Cousinia species. This clearly reveals application of ISSR molecular markers in taxonomy and species differentiation. Based on ISSR and morphological data, the members of two sections Cynaroideae Bunge and Platyacanthae Rech. f. are separated from each other. The Mantel test performed between morphological distance and Nei genetic distance produced non-significant correlation. This result also supports distance analyses of the trees and reveals that the two dendrograms are not correlated. One of the possible causes of this discordance between the two morphological and genetic trees can be reticulation and horizontal gene transfer (HGT) between closely related species.

Keywords

• Cousinia
• Cynaroideae
• ISSR
• morphometry