Swedish born explorer, geologist, naturalist and conservationist who emigrated to the United States in 1868. Turning from his original career as prospector, he studied botany and published mainly on the flora of the western States. In 1893 he was employed by F.V. Coville of the U.S. Department of Agriculture as a field assistant to J.H. Sandberg. His interest in bryology fostered a lifelong friendship with Elizabeth Britton, bryologist at Columbia College in New York, who later distributed bryophyte exsiccatae of Leiberg. Four years later he transferred to United States Geological Survey (1897) to work on the Forest Reserves of the Pacific northwest, though he still collected for the USDA. A particular concern of his was the devastating effects of fire arising from poor forest management practices and of over-grazing. His last post in government service took him to the Philippines (1905-1906) as Forest Inspector for the Insular Forest Service in Luzon. Before he died, Leiberg gave his personal herbarium to the University of Oregon (ORE); original collections for his governmental work are at US. Bryophyte material acquired by K (1890) was later transferred to BM (c. 1961) under the terms of the Morton Agreement. Moss exsiccatae from Idaho are also at BM. Nymphaea leibergii Morong is one of the many taxa named in his honour.