Temperature is a key environmental signal regulating germination. A thorough understanding of how seed populations respond to various temperatures can inform end-users regarding effective establishment strategies and forms the basis for questions related to a taxon's thermo-biology. Although abundant information exists regarding germination responses of economically important crops to several temperature scenarios, much less is known concerning the seed biology of wild germplasm. To address this, we examined the germination response of non-dormant Rudbeckia mollis seeds to various doses of constant or simulated seasonal diel temperatures. Germination response was sigmoidal. Seeds of R. mollis were capable of germinating within a few days to high percentages (>95%) at relatively cool constant (15–25°C) or 12-hour alternating (22/11–33/24°C) temperatures, with optimum temperatures for germination occurring at 25°C or 29/19°C. Germination was inhibited as temperatures increased to 30°C or 33/24°C with early and late germinating phenotypes displaying differential responses at these temperatures. No germination occurred at 35°C. Results are discussed in terms of seedling establishment of R. mollis outside its natural range and implications of climate change on germination.