13th Conference on Medicinal and Aromatic Plants of Southeast European Countries (CMAPSEEC 2026)

Background: Teucrium montanum and T. capitatum are closely related species inhabiting karst habitats of the coastal and peri-coastal regions of Croatia. In zones of syntopy, spontaneous hybrids described as T. × rohlenae K. Malý have been reported; however, the extent and evolutionary consequences of hybridization remain insufficiently understood.
Materials and Methods: For genetic analyses, individual plants were sampled from six syntopic localities in the Dalmatian hinterland. Based on morphological characteristics, plants were identified as T. montanum, T. capitatum, or putative hybrids. Samples were genotyped using 10 microsatellite loci developed through next-generation sequencing and the joint identification of microsatellite motifs in both species. Population structure was inferred using STRUCTURE, and individual hybrid class assignment (parental classes, F1, F2, BC1, BC2) was conducted using NewHybrids.
Results: Hybrid individuals were identified in five of the six syntopic localities, although their frequency varied considerably among populations. STRUCTURE analysis assigned the majority of T. montanum and T. capitatum individuals to distinct genetic clusters, whereas putative hybrids exhibited a broad range of admixture proportions between the parental clusters. Assignment to hybrid classes revealed that many individuals morphologically identified as T. montanum or T. capitatum were classified as late-generation hybrids, particularly F2 individuals and backcrosses.
Conclusions: The observed patterns do not support homoploid hybrid speciation as the primary evolutionary outcome of hybridization between T. montanum and T. capitatum. Instead, the prevalence of late-generation hybrids, extensive introgression, and evidence of ongoing gene flow point to a dynamic hybrid zone characterized by recurrent and cryptic hybridization.