Tremuloides (Fruiting Specimens): Answers to key questions in Conifers & Catkin-Bearing Trees and Shrubs of Saskatchewan, Fascicle 5, Flora of Saskatchewan by George Argus, Vernon Harms, Anna Leighton and Mary Vetter leading to this species. 

	capsules usually 2-valved; NOT [capsules usually 3- or 4-valved]
	capsules lanceoloid to narrowly ovoid, (2) 2.5-4.5 (7) mm; fruiting pedicles to 2 mm; petioles strongly laterally flattened at least distally; NOT [capsules ovoid to spherical, 3-8 mm; fruiting pedicels to 3.5 mm; petioles terete or somewhat flattened in the same plane as the blade]

Populus: Answers to key questions in Conifers & Catkin-Bearing Trees and Shrubs of Saskatchewan, Fascicle 5, Flora of Saskatchewan by George Argus, Vernon Harms, Anna Leighton and Mary Vetter leading to this genus.

trees; buds covered by 3-10 scales, usually resinous;  catkins pendulous, sessile; floral bracts deeply cut; perianth reduced to a non-nectariferous, cup-shaped or shallow saucer-shaped floral disc; stamens 6-60 (70); capsules 2-4 valved, narrowly ovoid to spherical, with the floral disc persistent at base; NOT [shrubs or trees; buds covered by 1 scale, not resinous; catkins erect, spreading, or +/- pendulous, sessile or terminating flowering branchlets; floral bracts entire, erose, bifid, or irregularly toothed; perianth reduced to an adaxial nectary (rarely also an abaxial nectary, then the 2 nectaries distinct or connate into a shallow cup); stamens 1, 2, or 3-10; capsules 2-valved, obclavate to ovoid or ellipsoid]