Achene Development of Canada Thistle and Perennial Sowthistle

Canada thistle was named Carduus arvensis by Tabernaemontanus in 1687, Cirsium arvense by Tournefort in 1700, Serratula arvensis by Linne in 1753, Cirsium arvense by Scopoli in 1772, Carduus arvensis by Robson in 1777 and Cnicus arvensis by Hoffman in 1804. The name Cirsium arvense Tourn. was adopted, but more recently Canada thistle has been referred to as Cirsium arvense (L.) Scop. The cardinal number of chromosomes for the Cirsium genus is 17.