Over 65 lineages of flowering plants have independently evolved the C4 photosynthetic pathway as a CO2-concentrating mechanism. Among these clades, there exists a gradient of intermediate character states between the ancestral, C3, and the derived, C4, pathways. These ‘C3-C4 intermediates’ represent transitional species and offer unique insights into the evolution of C4 photosynthesis. Current understandings of the physiology of C3-C4 plants suggest that they are found in areas that promote high levels of photorespiration and stomatal closure. These environments have been broadly described as low-CO2/high-O2, hot, dry, bright and/or saline; however, other factors, such as seasonal variations in temperature and precipitation, must be considered to fully describe the geographic range of each species. Using occurrence records obtained from the Global Biodiversity Information Facility (GBIF), this study aims to better define the ecological niches of C3-C4 species. Centers of high C3-C4 intermediate diversity are delineated with Geographic Information Systems (GIS) using an ecoregions-based approach. The climates of these centers are summarized with an average monthly time series for several atmospheric variables using historical raster files sourced from WorldClim. Here we find support that hot climates with seasonal precipitation favor C3-C4 species, though other contributing factors are usually involved. The centers of diversity, and their climates, contribute to the knowledge of the environments that are associated with a complex, primary metabolic trait.