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).
The genus Cousinia Cass. of the tribe Cardueae with about 700 species is one
of the most diverse genera in Central and SW Asia following Senecio and
Vernonia. The section Cynaroideae with 89 species is the largest section of
the genus. Cousinia calocephala is the only endemic species of the section
distributed in 14 provinces of Iran from Alborz to Zagros mountains. In
present study 65 plant specimens of 13 geographical populations of C.
calocephala were investigated based on the morphological and genetic (ISSR)
data. ANOVA test revealed a significant morphological difference among the
studied populations. Similarly, AMOVA test yielded a significant genetic
difference between the studied populations, suggesting that the studied
populations are morphologically and genetically differentiated. AMOVA test
revealed that 94% of the total genetic difference was due to
inter-populations genetic differences, while 6% was due to within-species
genetic variability. The discriminating power of ISSR loci as determined by
Gst against Nm analysis, revealed that almost all ISSR loci have an
excellent discriminating power. Thus, ISSR markers are efficient in
differentiating of the studied C. calocephala populations. The mantel test,
revealed a significant positive correlation between genetic and
morphological distance and geographical distance of the studied populations.
Genetic analysis results revealed that along with genetic drift, low level
of gene flow and migration, adaptive loci also helped populations diverge
and adapt these populations to their local condition. Thus, we have three
different groups which can be considered as three ecotypes for C.
calocephala based on the morphological and genetic data.
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