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

	some branches ending in a short thorn
	flowers 4-merous; NOT [flowers 5-merous]

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

	leaves pinnately veined; NOT [leaves 3-nerved from the base]
	flowers axillary, in few-flowered umbels or solitary; NOT [flowers numerous in a dense terminal panicle]
	fruit juicy; NOT [fruit dry]

Rhamnaceae: Answers to key questions in Flora of Alberta  leading to this family. 

	plants not parasitic on coniferous trees; NOT [plants parasitic on the trunks and branches of coniferous trees (pines)]
	trees or shrubs; NOT [herbs]
	plants 5-20 dm tall; NOT [plants 1-2 (5) dm tall]
	leaves simple, not lobed; NOT [leaves pinnately compound or palmately lobed]
	leaves ovate to elliptic; NOT [leaves needle-like]
	leaves 3-10 cm long; NOT [leaves 0.5-1.0 cm long]
	flowers perfect, or, if imperfect, the plants herbaceous, or, if woody, the flowers not in catkins; NOT [flowers imperfect, the staminate, and generally the pistillate too, in catkins; trees or shrubs]
	perianth uniseriate (i.e. of only one series of appendages all more or less the same) or entirely absent; NOT [perianth biseriate (i.e. of two different series of appendages, the inner generally larger, coloured, the outer generally smaller, greenish)]
	ovary superior; NOT [ovary inferior or partly so, or closely enclosed by the calyx and appearing inferior]
	fruit berry-like, black; NOT [fruit winged]