Heliotropium thermophilum Kit Tan, A. Celik & Y Gemici (Boraginaceae), is described as a species new to science and illustrated. Its diploid chromosome number of 2n = 16 is a first report. It is restricted to the province of Aydin bordering on Denizli in SW Anatolia and is of interest on account of its unusual habitat, which is a geothermal area with ground temperatures of 55-65 degrees C. Affinities clearly lie with the annual H. hirsutissimum Grauer, which is distributed in N Africa, the East Mediterranean area, and SW Asia; the latter, however, is hexaploid (2n = 48) and never occurs in thermal habitats. Micromorphological, ecological, and ecophysiological data for the new taxon are provided. Ecological isolation has allowed the evolution and differentiation of a new and distinct species.