A comparative study of the anatomy of <i>Noccaea aucheri</i> (Brassicaceae) species complex

The three endemic species, Noccaea aucheri , N. sempervivum and N. mummenhoffiana , previously classified in the genus Pseudosempervivum and investigated for the first time in this study as the Noccaea aucheri species complex, present considerable taxonomic challenges due to overlapping morphological characters. This study provides the first comprehensive anatomical analysis of this species complex, examining 45 anatomical characters from 15 populations under different ecological conditions in Turkey. Root, stem, leaf and stomatal traits were investigated through light microscopy, and anatomical data were analysed by cluster analysis in combination with bioclimatic variables. The results show that anatomical characters such as root diameter and sclerenchyma thickness partially distinguish N. sempervivum from other taxa, but do not differentiate between N. aucheri and N. mummenhoffiana . The presence of myrosin cells, calcium oxalate crystals and variation in stomatal index appears to be more influenced by the environment than by taxonomy. Overall, the anatomical data showed significant variation among the three species, but no clearly diagnostic traits, reinforcing the hypothesis that these taxa may actually represent a single polymorphic species.