Since this key is different in the method by which it is used, a few words of explanation are in order. First, one should strive to obtain normal-growing twigs for identification. Branch tips should be in high light. Observations should not be made on a single leaf or twig; study several to be sure they are uniform and characteristic of the plant.
To determine the identification of a plant, turn to the Key to Classes, Groups, Subgroups, and Genera. First, decide between the two classes: A) leaves evergreen or B) leaves deciduous. Since all the evergreen trees included in this key are narrow-leafed with needlelike leaves, narrow-linear, or awl-shaped, there should be no difficulty in distinguishing them from deciduous or broad-leafed plants.
Assuming that the first choice was for a deciduous plant, and using red oak as an example (Quercus rubra), turn to Class B, leaves deciduous. Then a decision is made between the two groups: (I) leaves opposite or whorled or (II) leaves alternate. The red oak has alternate leaves and therefore is in Group II, leaves alternate. A decision must now be made between the four subgroups: (I) leaves compound, (II) leaves lobed, (III) leaves toothed, or (IV) leaves entire. Since the leaves of the red oak are lobed, it will fall in Subgroup II.
In starting the identification in Subgroup II, notice that although there are always two or more alternatives, only one will satisfy the characteristics of the plant in question (this will also be true with the other subgroups). The first alternative is: I) lobes are entire and not regularly toothed. The second alternative is: II) lobes toothed. Since I) satisfies the characteristics of the red oak, we go to: A. buds are not clustered at the end of the twigs, or the alternative, AA. buds are clustered at the ends of the twigs. AA. satisfies the characteristics of the red oak and it keys out the genus as Quercus, the oaks.
For the key to the oak species, turn to page 84. Here the first order is I. leaves are lobed. The alternative is II. leaves are not lobed. It was previously determined that the leaves were lobed, so move to: A. lobes of the leaves end in bristles, or its alternative, AA. lobes are rounded and are without bristle-like points. Since A. satisfies the characteristics of the red oak, go to the next order: ||. leaves elliptic to oblong is correct. On to the next order, aa. is correct for the red oak, so move on. Here, ii. is correct. Finally, you will find AA) is correct, and it keys out to Quercus rubra maxima, the eastern red oak.