American speedwell. Photo by: Mary Ellen (Mel) Harte, , Bugwood.org

Henbit deadnettle. Photo by: Steve Dewey, Utah State University, Bugwood.org

Hairy bittercress. Photo by: Dan Tenaglia, Missouriplants.com, Bugwood.org

Henbit deadnettle seedling. Photo by: Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org

Downy brome (Cheatgrass). Photo by: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

European field pansy (field violet). Photo by: Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org

Purple deadnettle. Photo by: Richard Old, XID Services, Inc., Bugwood.org

Canadian horseweed. Photo by: Richard Old, XID Services, Inc., Bugwood.org

Field violet (European field pansy). Photo by: Richard Old, XID Services, Inc., Bugwood.org

Common Chickweed. Photo by: Richard Old, XID Services, Inc., Bugwood.org

Annual rygrass. Image found at http://www.agry.purdue.edu/turf/tips/2005/cale49.htm and was by Cale Bidgelow.