Chapsa rubropruinosa Messuti & Codesal collected in Argentina is described as new to science. The species is characterized by a thin thallus, apothecia with a pigmented disc, and transversely septate, hyaline, non-amyloid to faintly amyloid ascospores with thin cell walls. Chapsa minor is recorded for the first time from South America. The new combination Topeliopsis lomatiae (Messuti, Lumbsch & Vězda) Messuti & Mangold is proposed.