Lepidium barnebyanum is a rare species of flowering plant in the mustard family known by the common names Barneby's pepperweed, Barneby's pepper-grass, and Barneby's ridge-cress. It is endemic to Utah, where there is a single population in Duchesne County. It is a federally listed endangered species of the United States. There is one known population of this plant containing about 5000 individuals. The population occurs on a shale substrate that is popular with off-road vehicle enthusiasts whose vehicles damage the habitat. Petroleum exploration is also a threat.