Taxonomy and biogeography of various lecideoid saxicolous genera of lichenized ascomycetes (roughly the saxicolous members of Lecidea in Zahlbruckner’s very wide, old concept). The family Lecideaceae (in its recent circumscription) is in the centre of my recent studies. My biogeographical studies are mainly focused on the areas with cool climates (polar and subpolar regions and alpine belts of mountain ranges of both hemispheres). Another area of interest is the history of the Botanische Staatssammlung, its collections and collectors.
- Lecidea and other saxicolous lecideoid genera for “Lichen Flora of the Greater Sonoran Desert Region”
- Lecideoid saxicolous lichens of Tajikistan (with I. Kudratov, Dushanbe)
- Lecideoid saxicolous lichens from the Bering Strait Region (with M. Andreev, St. Petersburg)
- The Lecidea atrobrunnea complex in the Americas (with C. Leuckert, Berlin)
- Lecideoid saxicolous lichens once collected by Henry A. Imshaug in the alpine belt of the Western United States and adjacent Canada as well as in Patagonia
- Lecideaceae Exsiccatae
- Type collections in the lichen herbarium of the Botanische Staatssammlung