Conyza canadensis
Canadian Horseweed (Conyza canadensis) is species of plant.  It is also known as Canadian Fleabane, Coltstail, and Marestail.  It belongs in the family Asteraceae.  It is native to North America and Central America.  It has been naturalized in Alaska and Hawai'i.  It blooms from June to September.  This species is found in prairies, fields, along roadsides, gardens, and stream edges.  It has a height of 3 inches to 10 feet.