Bull Thistle flower (Cirsium vulgare) with a crowd of visitors at Big Hollow Recreation Area in Des Moines county Iowa.

Details: Canon EOS 10D,  shutter 1/200 second, aperture f11, ISO 400, Canon EF 100 mm macro lens, Canon MR-14EX flash on

Selected References:

Lim, Rodney G, Christianson, Katheryn M. "Bull thistle [Cirsium vulgare (Savi) Tenore]" The Thistles of North Dakota W-1120, October 1996" <http://www.ext.nodak.edu/extpubs/plantsci/weeds/w1120/w1120w.htm > (12 Sep. 2004).

Thieret John W, Niering William A, and Olmstead Nancy C. National Audubon Society Field Guide to North American Wildflowers, Eastern Region. New York: Alfred A. Knopf, Inc. Plate 542, P 384-385.

USDA-NRCS. "Plant profile for Cirsium vulgare." The PLANTS Database (http://plants.usda.gov/ ). National Plant Data Center, Baton Rouge, LA 70874-4490 USA. 2004.  <http://plants.usda.gov/cgi_bin/plant_profile.cgi?symbol=CIVU  > (12 Sep. 2004).