Ethnobotany of Horseradish (Armoracia rusticana, Brassicaceae) and Its Wild Relatives (Armoracia spp.): Reproductive Biology and Local Uses in Their Native Ranges. Horseradish (Armoracia rusticana) has been cultivated for its root for over 2,000 years. Today, commercial production takes place primarily in North America and Europe where A. rusticana is propagated exclusively vegetatively. Like many vegetatively-propagated crops, cultivated A. rusticana plants are generally sterile. Armoracia rusticana is one of three species in the genus: A. macrocarpa is native to the Central Danube River Basin, A. rusticana is putatively native to Eastern Europe, and A. sisymbrioides is native to Siberia. Documenting the ways in which the three Armoracia species are used in their putative native ranges and the reproductive biology of Armoracia in these regions will advance understanding of the role of humans in the evolution of sterility in A. rusticana. In this broad-scale ethnobotanical analysis, we document 1) which Armoracia species are used in different geographic regions, 2) the reproductive biology of cultivated and natural Armoracia populations, and 3) the uses of Armoracia species in their native areas. Fieldwork was conducted in Austria, Bulgaria, Romania, and Russia. Ethnobotanical data were collected through written questionnaires. In all areas visited, A. rusticana is the primary Armoracia species; however, there is regional variation in the way the plant is used. Armoracia rusticana is propagated vegetatively and is not found in the wild. Armoracia macrocarpa and A. sisymbrioides reproduce by seed in nature. These data provide an understanding of contemporary uses and management strategies of Armoracia species in their native ranges, demonstrate the differential reproductive biology of a clonally-propagated crop relative to its wild progenitors, and emphasize the importance of ethnobotanical data collection for crops and their wild relatives from a broad geographic range.