Herpothallon rubroechinatum is described from the U.S.A. (Florida), Costa Rica and Peru. The new species is characterised by scattered red anthraquinone crystals being attached to hyphae projecting from the thallus, the globose to cylindrical pseudoisidia, a closely adnate thallus, and psoromic acid as the main lichen compound; pycnidia are common at the tips of the pseudoisidia. The medulla of the new species shows a patchily distributed amyloid reaction. Contrary to previous reports, the amyloidity of the medulla was observed in all Herpothallon species re-investigated during this study. H. rubroechinatum is compared to the two other red pigmented species that contain psoromic acid, H. australasicum that lacks pigment crystals on the pseudoisidia, and H. globosum that has a loosely attached thallus and a well developed red hypothallus.