d. Trunk and large branches armed with stout spines; leaflets

3/4 - 1-1/2 inches long, GLEDITSIA, p. 165.

dd. Trunk and large branches unarmed; leaflets 2 - 2-1/2 inches long. GYMNOCLADUS, p. 163.

bb. Leaves opposite.

c. Leaves pinnately compound; fruit a samara.

d. Leaflets 3-5; samaras paired. ACER, p. 172.

dd. Leaflets 7-11, exceptionally 5; samaras not paired. FRAXINUS, p. 210.

cc. Leaves digitately compound; fruit a prickly bur. AESCULUS, p. 194.

WINTER KEY TO THE GENERA[B]

a. Leaves persistent and green throughout the winter, needle-shaped, awl-shaped or scale-like.

b. Leaves in clusters of 2-5, sheathed. PINUS, p. 5.

bb. Leaves solitary, not clustered.

c. Leaves opposite.