1. Ecogeographic isolation is a fundamental prezygotic barrier to reproduction and a step toward diversification in flowering plants. However, whether ecogeographic isolation acts as a reproductive barrier between species and thus as a mechanism for species divergence is unclear and is expected to change as species distributions shift under climate change. 2. Using a Maxent framework, we quantified the extent of ecogeographic isolation of nine closely related species of the European plant genus Pulmonaria, which lack pre-mating barriers and often form hybrids. We investigated ecogeographic isolation under both current conditions and four climate change scenarios; two unrelated future climate models, each with two predictions of the potential trajectories of climate change. 3. Compared with current climates, under these future climate scenarios, there will be an increase in mean annual temperature, but not in mean annual precipitation in the range of Pulmonaria throughout Europe. This will result in a range contraction in three of the nine Pulmonaria species, a range expansion in two species, and no clear effect of climate change on the ranges of four species. 4. Climate change will result in an overall increase in ecogeographic isolation between these species in future. In particular, species that have low ecogeographic isolation under current conditions are predicted to increase the most in their ecogeographic isolation under climate change. 5. Synthesis These results highlight that climate change can strongly impact on a major premating barrier of closely related species, therefore potentially affect the evolutionary trajectory of plants in the future.