The first 4 levels of the US Soil Taxonomy hierarchy (soil order, suborder, greatgroup, subgroup), presented as a data.frame (de-normalized) and a list of unique taxa.
data(ST)An object of class data.frame with 2665 rows and 4 columns.
Soil Survey Staff. 1999. Soil taxonomy: A basic system of soil classification for making and interpreting soil surveys. 2nd edition. Natural Resources Conservation Service. U.S. Department of Agriculture Handbook 436. https://www.nrcs.usda.gov/wps/portal/nrcs/main/soils/survey/class/taxonomy/
Soil Survey Staff. 2014. Keys to Soil Taxonomy, 12th ed. USDA-Natural Resources Conservation Service, Washington, DC. https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/survey/class/taxonomy/?cid=nrcs142p2_053580