Arvense: Answers to key questions in Budd's Flora and Flora of Alberta leading to this species. 

	perennial plants
	plants from deep creeping rootstocks; NOT [plants without creeping rootstocks]
	male and female flowers on separate plants; NOT [male and female florets on the same plant or flower head]
	bracts of involucre only slightly, if at all, cobwebby, and if so the inner bracts twisted and not spine-tipped; NOT [bracts of involucre covered with cobwebby hairs, and all bracts spine-tipped]
	heads small, less than 2.5 cm high; NOT [heads larger, more than 2.5 cm high]
	involucres 1-2 cm high; NOT [involucres more than 2 cm high]
	involucres rarely over 12 mm wide; NOT [involucres usually more than 12 mm wide]

Cirsium: Answers to key questions in Budd's Flora  and Flora of Alberta leading to this genus. 

	juice watery; NOT [juice milky]
	leaves with spiny margins
	bracts of involucre not dry or parchmenty, usually green; NOT [bracts of involucre dry, parchmenty or membranous, not green]
	some involucral bracts spiny-tipped
	involucral bracts without hooked bristles
	receptacle densely bristly; NOT [receptacle naked]
	flower heads with all florets tubular
	stamens united to form a tube around the pistil
	pappus present, distinct; NOT [pappus none or inconspicuous]
	pappus of capillary bristles; NOT [pappus of scales, or of awns, or a crown or none]
	pappus bristles much longer than achene; NOT [pappus hairs not longer than achene]
	pappus bristles plumose; NOT [pappus bristles naked or merely minutely barbellate]