Michigan Trees: A Handbook of the Native and Most Important Introduced Species
cc. Buds and twigs not conspicuously white-downy; twigs
usually red-brown.
d. Terminal buds about 1/8 inch long, puberulous, dusty-looking; lateral buds widely divergent; twigs rather coarse. _P. grandidentata_, p. 51.
dd. Terminal buds about 1/4 inch long, glabrous, lustrous; lateral buds more or less appressed; twigs rather slender. _P. tremuloides_, p. 49.
bb. Terminal buds 1/2-1 inch long, sticky-resinous.
c. Terminal buds about 1/2 inch long; buds not fragrant; twigs usually yellow, more or less strongly angled. _P. deltoides_, p. 57.