Canada Thistle (Cirsium arvense) Division - Magnoliaphyta Class - Magnoliopsida Subclass - Asteridae Order - Asterales Family - Asteraceae Genus - Cirsium Canada thistle can be differentiated from musk and bull thistle by the fact that it has no spiny bracts or spines on the stems. In appearance, it falls between bull thistle and a centaurea. Its spineless bracted flower-head resembles that of a centaurea. Weeds Taxonomic List List by Scientific Name List by Common Name