Vondrák, J., Palice, Z., Mareš, J. & Kocourková, J. 2013. Two superficially similar lichen crusts, Gregorella humida and Moelleropsis nebulosa, and a description of the new lichenicolous fungus Llimoniella gregorellae. — Herzogia 26: 31–48.
Although some characters distinguishing Gregorella humida and Moelleropsis nebulosa were previously known, sterile specimens and specimens with poorly-developed apothecia are often difficult to separate. We provide morphological and anatomical characters that will allow reliable determination of such difficult collections. The most important character for determination of sterile thalli is the shape of the mycobiont cells in the thallus granules. A key summarizes the diagnostic characters of G. humida and M. nebulosa (and some similar species). The Nostoc photobiont in G. humida is morphologically similar to Nostoc from M. nebulosa but the two are not closely related within the genus. The ecology of both lichen species is similar, but there are differences in the preference for differently acidic substrates and in co-occurring bryophytes and lichens. In Central Europe, M. nebulosa was frequently collected in the first half of the 20th century, but there are few recent records, whereas G. humida was only occasionally collected before the last two decades, but is now regularly collected. Moelleropsis nebulosa rarely hosts lichenicolous fungi, though we have seen Lichenochora mediterranae (previously known only on Fuscopannaria) and Sarcopyrenia sp. on it. Gregorella humida rarely hosts a single lichenicolous fungus, described here as Llimoniella gregorellae, spec. nova, which causes obvious harm to host thalli; ITS sequences indicate that it belongs in Leotiomycetes.