Recently, nine species of lichenicolous fungi were found growing on Cetraria aculeata (Parmeliaceae) in a sand dune system in the Ukraine. One of them, Didymocyrtis trassii, is described here as new to science. This species is similar to D. pseudeverniae but differs in having smaller pycnidia, smaller obpyriform to clavate conidia as well as its DNA sequence. The new monotypic lichenicolous genus Katherinomyces is described here. Acremonium lichenicola s. l., Eonema pyriforme, Didymocyrtis cladoniicola and Lichenoconium erodens are reported for the first time on Cetraria aculeata. Furthermore, E. pyriforme is reported for the first time from lichen thalli. Acremonium lichenicola, E. pyriforme and Taeniolella rolfii are new for the mycobiota of the Ukraine. A key to the eleven known lichenicolous species on Cetraria aculeata is provided.