Stirtonia byssoidea, S. coei and S. latispora, all from coastal hammocks within Everglades National Park, are described as new to science. Stirtonia byssoidea is characterized by a felty byssoid thallus, conspicuous immersed white pruinose-like lirelliform ascigerous zones, small ascospores and the presence of perlatolic acid. It is closest to S. alba but has a different thallus type and much smaller ascospores. Stirtonia coei is recognized by its lirellate ascigerous zones raised well above a greyish crystallate thallus, large ascospores and a lack of chemistry. It is closest to S. curvata but differs by its I+ blue thallus, strongly raised ascigerous zones and by having no lichen substances. Stirtonia latispora can be identified by its white lirelliform ascigerous areas immersed in a greyish green thallus, large, broad ascospores with a conspicuously enlarged mid cell and lack of substances. It would also key out close to S. curvata but differs by the aforementioned ascigerous zones, an I+ blue thallus, wider ascospores with a different locular configuration and its lack of chemistry. A key to the six species known from the Neotropics is also provided.