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

	plants glabrous or sparsely pubescent; NOT [plants densely hairy throughout]
	leaflets 3-5; NOT [leaflets 5-9], NOT [leaflets 7-17]
	leaflets narrowly linear; NOT [leaflets linear-oblong]
	leaflets 1-1.5 mm wide; NOT [leaflets 2-3 mm wide]
	calyx villose-tomentose; NOT [calyx glabrous except the lobes]
	flowers rose or purple; NOT [flowers white]

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

	herbs; NOT [shrubs]
	the root tuber-like
	plants not climbing
	leaves pinnately divided; NOT [leaves palmately divided]
	the terminal leaflet normal; NOT [the terminal leaflet replaced by a tendril]
	leaves glandular-dotted
	flowers in dense, cylindrical spikes; NOT [flowers in racemes]
	flowers small, to 5mm; NOT [flowers 10-15 mm long]
	keel not truncate; NOT [keel mostly truncate]
	stamens 5; NOT [stamens 10]
	pods not segmented or jointed; NOT [pods segmented or jointed, breaking up at maturity]
	pods not prickly; NOT [pods with hooked prickles]

Leguminosae: Answers to key questions in Budd's Flora  leading to this family. 

	herbs; NOT [shrubs or trees]
	plants terrestrial or semiaquatic; NOT [plants aquatic; leaves submerged or floating]
	plants NOT with colored milky juice
	plants with more than one normal leaf
	some or all leaves alternate; NOT [leaves opposite, whorled, or basal]
	leaves with stipules; NOT [leaves without stipules, or having glands]
	flowers with two floral rings, and with each petal distinct from the others]
	calyx regular; NOT [calyx irregular, some sepals smaller than others]
	flowers irregular in shape
	corolla pea-like; NOT [corolla with one petal spurred or sac-like]
	stamens usually separate or partly so, not in a column; NOT [stamens numerous, united into a column]
	fruit a legume; NOT [fruit a 3-valved capsule]