Objective: The genus Linaria Mill. (Plantaginaceae) represents a taxonomically complex group characterized by high morphological similarity and extensive intraspecific variation, which often complicates the delimitation of species.
Method: In this study, four taxa belonging to the Linaria lineolata s.s. complex (Linaria lineolata, Linaria elymaitica, Linaria karajensis, and Linaria khalkhalensis) were investigated using an integrative approach that combined morphological and molecular data. A total of 20 quantitative and qualitative morphological characters were analyzed using univariate statistics and Principal Component Analysis (PCA). To investigate molecular relationships, sequences of the low-copy nuclear gene AGT1 and the chloroplast intergenic spacer rpl32–trnL were analyzed, and phylogenetic relationships were reconstructed using Bayesian inference.
Results: The PCA results revealed a clear separation among the studied taxa, with the first two principal components explaining a substantial proportion of the total variance. Molecular phylogenetic analyses based on the nuclear gene AGT1 and the chloroplast intergenic spacer rpl32–trnL further supported the delimitation of the studied taxa, revealing distinct and well-supported clades.
Conclusions: A dichotomous identification key was also constructed using the most diagnostic morphological characters. The congruence between morphological and molecular datasets indicates clear taxonomic independence among the investigated species. These findings provide evidence for the delimitation of species boundaries within the L. lineolata s.s. complex and highlight the effectiveness of an integrative taxonomic approach in resolving species complexes within Linaria.