Astrochapsa martinicensis is described as new to science. It is characterized by a whitish-farinose thallus, 6–8-spored asci, (4–)5–7(–9)-septate ascospores of (12.5–)14–24(–29) × (4.5–)5–6.5(–7) µm and a chemistry with one terpenoid and traces of UV+ substances. The new species was discovered among lichen specimens collected in 2013 on the island of Martinique (Lesser Antilles). A phylogenetic analysis using nuLSU sequences places the new species in the genus Astrochapsa, as sister species to an unidentified specimen from Venezuela. An identification key to all currently accepted Astrochapsa species is provided.