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

	thorns stout and short; NOT [thorns long]
	leaves nearly glabrous beneath, more or less pubescent above; NOT [leaves pubescent beneath, at least on the veins]
	sepals short, triangular, acute but not attenuate; NOT [sepals attenuate, long-pointed] (BF)
	sepals ovate; NOT [sepals lanceolate, acuminate] (FOA)
	sepals hairy above
	sepals often without glands; NOT [sepals glandular-margined]
	fruit black or deep purple when ripe; NOT [fruit red or red-purple]
	nutlets pitted

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

	shrubs or trees; NOT [herbs, or with a woody base and otherwise herbaceous]
	plants taller; NOT [creeping dwarf shrubs]
	stems with stout thorns; NOT [stems not thorny]
	spines never leafy; NOT [spines leafy in the first year, leafless thereafter]
	leaves simple; NOT [leaves compound or lobed]
	leaves mostly incised-toothed or lobed; NOT [leaves entire to toothed]
	flowers usually more numerous; NOT [flowers solitary on a long peduncle]
	NOT [flowers in broad compound corymbs]
	ovary inferior; NOT [ovary or ovaries superior]
	ovary enclosed in and adnate to the hypanthium; NOT [hypanthium shaped like a saucer, cup or urn and free from the ovary]
	fruit a pome but often berry-like

Rosaceae: 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
	flowers regular in shape; NOT [flowers irregular in shape]
	calyx regular; NOT [calyx irregular, some sepals smaller than others]
	stamens usually separate or partly so, not in a column; NOT [stamens numerous, united into a column]
	ovary of one or more carpels, either separate or enclosed by a fleshy receptacle; NOT [ovary of 5 united carpels]