An inconspicuous lichen with immersed thallus and large black perithecia. The species is characterised by melanised, 5–7-septate, thick-walled ascospores with round cell lumina. The associated Trentepohlia algae in the thallus are visible only in the cross-section of a host tree bark. Therefore, although the species is lichenized, it resembles non-lichenized fungi. Potentially, the lichen may be mistaken for Requienella seminuda that has very similar but 5-septate spores, non-lichenized thallus and perithecia with a prominent beak-shaped protrusion around the ostiolum.
Lithothelium septemseptatum grows on rough bark of deciduous trees (oaks, ash trees, willows) in forests with humid mesoclimate (such as scree and floodplain forests). In Europe, it has been reported mainly from lowlands and uplands. In central Europe, it is rare. Up to now, only one finding is known from the Czech Republic, concretely from the Křivoklát region (Týřov).taxonomic classification:
All records: 3, confirmed 3. One click on a selected square displays particular record(s), including their source(s).