Michigan Trees: A Handbook of the Native and Most Important Introduced Species
c. Leaves about 1 inch long, divergent; cones sessile,
pointing forward towards the tip of the branch, persistent 10-15 years, opening very unevenly. _P. banksiana_, p. 9.
cc. Leaves 1-1/2-3 inches long, slightly divergent; cones stout-stalked, pointing away from the tip of the branch, maturing in second season, opening evenly. _P. sylvestris_, p. 13.
bb. Leaves 3-6 inches long.