Arethusa: Answers to key questions in Lilies, Irises & Orchids of Saskatchewan by Vernon L. Harms and Anna L. Leighton leading to this genus. The answers are in the order you would normally work through the key. 

	Plants green, with at least some green leaf-blades, these sometimes early withering or late developing; flowering stems green (pale pink to purplish-red in Calypso bulbosa), bearing sheathing bracts in some species; rootstocks not coral-like; capsules spreading to erect (occasionally drooping when old); NOT [Plants non-green saprophytes lacking leaf-blades; flowering stems yellowish to purplish-red or brown (pale greenish-yellow in C. trifid), bearing sheathing bracts; rhizomes rootless, coral-like in their branching; capsules drooping]
	Flowers 1 to 2 per stalk (occasionally more in Cypripedium reginae and C. montanum), large, showy; lip 1 cm long or longer, either inflated or broad and flat; NOT [Flowers 3 or more in a spike-like inflorescence, small, often inconspicuous; lip usually less than 1 cm long, but if longer, neither inflated nor broad and flat]
	Lip broad and flat, not inflated; flower subtended by a pair of minute, scale-like floral bracts; leaf single, emerging during or after flowering from upper sheathing bract on stem, linear, grass-like, 2-4 mm wide, folded lengthwise; NOT [Lip inflated, a slipper-like or sac-like pouch; flower subtended by a single, large, usually leaf-shaped floral bract; leaves usually 2 or more, present at flowering-time, (in Calypso bulbosa the broad, basal leaf that is produced the previous fall, may or may not be present at flowering time)]

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

	plants NOT aquatic
	flowers irregular; NOT [flowers regular]
	perianth present, conspicuous, in two series of 3 segments, often brightly colored; NOT [perianth absent or inconspicuous]
	perianth usually large, consisting of sepals and petals usually alike, variously colored; NOT [perianth small, consisting of 3 green sepals and 3 whitish petals]
	petals NOT deciduous
	stamens 1 or 2; NOT [stamens 3 or 6]