A refined species concept in the tropical lichen genus Polymeridium (Trypetheliaceae) doubles the number of known species, with a worldwide key to the species

A refined species concept is applied in the tropical corticolous lichen genus Polymeridium (Trypetheliaceae). While up to now many species were considered to be variable in phenotypical characters, such as hamathecium inspersion and/or presence of lichexanthone, these characters are here accepted as species-specific characters. This classification is in line with the taxonomy in other groups of lichenized fungi. The monotypic genus Exillseptum is included here in Polymeridium, as it differs in only one character from several species of Polymeridium and has no unique characters. The number of accepted species is thus raised from 27 to 53, including 13 new species, viz.: Polymeridium albidoreagens, P albidovarians, P alboflavescens, P catapastoides, P. costaricense, P. inspersum, P. multiforme, P. multiseptatum, P. neuwirthii, P. pyrenastroides, P. submuriforme, P tribulationis, and P. xanthoreagens. The following new combinations are proposed: Polymeridium albopruinosum, P. amylosporum, P. bengoanum, P. brachysporum, P. jordanii, P. microsporum, P. ocellatum, refertum, P. siamense, P stramineoatrum, P. subvirescens, and P. suffusum. An identification key is provided to all accepted species.