Abstract
Two new species of Astrothelium are described from the Yungas forest in Bolivian Andes. Astrotheliumchulumanense is characterised by pseudostromata concolorous with the thallus, perithecia immersed for the most part, with the upper portion elevated above the thallus and covered, except the tops, with orange pigment, apical and fused ostioles, the absence of lichexanthone (but thallus UV+ orange-yellow), clear hamathecium, 8-spored asci and amyloid, large, muriform ascospores with median septa. Astrotheliumisidiatum is known only in a sterile state and produces isidia that develop in groups on areoles, but easily break off to reveal a medulla that resembles soralia. Both species, according to the two-locus phylogeny, belong to Astrothelium s.str. The production of isidia is reported from the genus Astrothelium and the family Trypetheliaceae for the first time.