Benson, L. 1982. The cacti of the United States and Canada.  Stanford, CA: Stanford University Press.

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Loflin, B. and Loflin, S. 2009. Texas Cacti. College Station: Texas A&M University Press.

Powell, A. M. and Weedin, J. F.  2004.  Cacti of the Trans-Pecos and adjacent areas.  Lubbock:  Texas Tech
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Powell, A. M. and Weedin, J. F. 2008. Cacti of Texas, a Field Guide. Lubbock: Texas Tech University Press.

Weniger, D.  1984.  Cacti of Texas and neighboring states.  Austin:  University of Texas Press.



Echinocereus Online:   http://www.echinocereus.de/

The Echinocereus Reference Collection:  http://www.lisowski58.freeserve.co.uk/

Vascular Plant Image Library:  http://www.csdl.tamu.edu/FLORA/gallery.htm

Cacti Guide.com:  http://www.cactiguide.com

Opuntiads of the USA:  http://www.opuntiads.com/index.html

Flora of North America:  http://www.efloras.org/flora_page.aspx?flora_id=1

Discover Life:  http://usmo4.discoverlife.org/

Patrick Alexander:  http://www.polyploid.net/

Joe Forks:  http://www.logojoe.com/

USDA, Natural Resources Conservation Service: http://plants.usda.gov/index.html