He described a number of new species, worked on systematic reorganization of botanical groups, and contributed greatly to the study of European flora.
He also helped create the Department of Biosystematics, and the journal Folia, published by the Geobotanical and Phytotaxonomic Institute.
He contributed to economic botany, especially with his work on the flora of Slovakia and the Czech Republic.
He also made substantial contributions to the studies of the fern genera Dryopteris, Lastraea, and Thelypteris.
Other plant genera he worked on included Helictotrichon, Avenula, Rubus and Crataegus.