Conyza canadensis

Conyza canadensis (sometimes called Erigeron canadensis L.) is an annual plant native throughout most of North America and Central America. It is also widely naturalized in Eurasia and Australia. Common names include horseweed, Canadian horseweed, Canadian fleabane, coltstail, marestail and butterweed. It was the first weed to have developed glyphosate resistance, reported in 2001 from Delaware.