Michigan Trees: A Handbook of the Native and Most Important Introduced Species
d. Twigs strictly glabrous; buds glabrous; spherical flower
buds clustered on the sides of the shoot; pith pink; large trees.
e. Twigs rank-smelling when broken; tip of outer bud-scales often apiculate; tips of branches curving upwards; bark separating into long, thin flakes loose at the ends. _A. saccharinum_, p. 185.
ee. Twigs not rank-smelling when broken; tip of outer bud-scales rounded; tips of branches not conspicuously curving upwards; bark rough-ridged, but seldom forming loose flakes. _A. rubrum_, p. 187.