BackgroundHistorical ethnobotanical studies are useful starting points for further diachronic analysis. The aim of this contribution is to present archival data from the Polish-Lithuanian-Belarusian borderland, which were collected by Adam Fischer, a Polish ethnographer from Lviv, in the 1930s. These data were originally gathered for publication in the first part of the Lexicon of Slavic beliefs and customs, dedicated to plant uses in traditional Slavonic culture. It was intended to be a joint international enterprise, but was never actually fulfilled.MethodsIn this article we used information from historical Lithuania (the Great Duchy of Lithuania), nowadays a border region between Poland, Lithuania and Belarus. We applied cultural importance indices such as Use Value, Relative Importance value and Sørensen similarity coefficient, in order to compare our data with a western Ukraine data set from the same research framework.ResultsIn total, 153 plant taxa were registered as used in peasant culture in the Polish-Lithuanian-Belarusian borderland in the 1930s. The species which achieved the highest Use Values were: Calendula officinalis, Cyanus segetum, Helichrysum arenarium, Betula sp., Prunella vulgaris, and Nuphar lutea or Lilium sp. The most salient use categories were medicinal, followed by food and home garden plants. The overall similarity to plants recorded in western Ukraine within the same project of Fischer’s is quite low (46%), which may be explained by the partly different flora found in the regions, and a cultural discontinuity, revealed by the difference in species with the highest UV. Moreover, the field collaborators were different in the two regions and may have paid attention to different cultural spheres of use.ConclusionsThe presented ethnobotanical data are a valuable contribution to the ethnobotany of Eastern Europe as a whole. In particular, the presented list of plants may be a rich source for future studies on the ethnobotany of the Polish diaspora in Lithuania, and diachronic studies in north-east Poland and Belarus.