Francis, John K., ed. 2009. Wildland Shrubs of the United States and its Territories: Thamnic Descriptions General Technical Report IITF-WB-1 U.S. Department of Agriculture, Forest Service International Institute of Tropical Forestry and Shrub Sciences Laboratory (online resource).
Online details: http://www.fs.fed.us/global/iitf/wildland_shrubs.htm