( Prairie wildflowers )

http://www.illinoiswildflowers.info/prairie/plant_index.htm

http://www.minnesotawildflowers.info/page/plants-by-name

http://www.extension.iastate.edu/Publications/SUL18.pdf

http://uipress.lib.uiowa.edu/ppi/index.php

http://uswildflowers.com/wfquery.php?State=IA

http://iowaplants.com/flora/family/Apocynaceae/asclepias/Asclepias.html