Michigan Trees: A Handbook of the Native and Most Important Introduced Species
cc. Bark of trunk gray to nearly black; cones maturing in
first season, 2-3 inches long; cone-scales thickened at the apex and topped with a short spine. _P. laricio austriaca_, p. 11.
+WINTER KEY TO THE SPECIES OF PINUS+
a. Leaves 5 in a cluster; cones 4-10 inches long. _P. strobus_, p. 7.
aa. Leaves 2 in a cluster; cones less than 4 inches long.
b. Leaves 1-3 inches long.