The end-Triassic event (ETE), a short global interval occurring at the end of the Triassic Period (similar to 201.5 Ma), was characterized by climate change, environmental upheaval, as well as widespread extinctions in both the marine and terrestrial realms. It was associated with extensive perturbations of the carbon cycle, principally caused by the volcanic emplacement of the Central Atlantic Magmatic Province in relation to the break-up of Pangea. The correlated change in atmospheric CO2 concentrations (pCO(2)) can be reconstructed with the stomatal proxy, which utilizes the inverse relationship between stomatal densities of plant leaves (here stomatal index (SI), which is the percentage of stomata relative to epidermal cells) and pCO(2). Fossilized Lepidopteris leaves are common and widespread in Triassic strata, thus offering great potential for high-resolution pCO(2) reconstructions. A dataset of leaf cuticle specimens belonging to the seed fern species Lepidopteris ottonis from sedimentary successions in Skane (Scania), southern Sweden, provided the possibility of pCO(2) reconstruction at the onset of the ETE. Here, we tested the intra- and interleaf variability of L. ottonis SI, and estimated the pCO(2) during the onset of the ETE. Our findings confirm L. ottonis as a valid proxy for palaeo-pCO(2), also when using smaller leaf fragments. Importantly, the statistical analyses showed that the SI values of abaxial and adaxial cuticles are significantly different, providing a tool to distinguish between the two sides and select cuticles for analysis. Reconstructed pCO(2) increased from similar to 1000 pre ETE to similar to 1300 ppm at the onset of the event, a significant increase of similar to 30% over a relatively short time period. The pCO(2) recorded here is similar to previously published estimates, and strongly supports the observed pattern of elevated pCO(2) at the onset of the ETE.