| 1a. Trees, with white or yellowish bark exfoliating in thin papery plates or scales [— 2.] | |
| 1b. Tree or shrub, with smooth, dark gray bark; trunk fluted with prominent longitudinal ridges | Hornbeam, Carpinus caroliniana. |
| 1c. Trees or shrubs; the bark more or less roughened, but not exfoliating; trunk not fluted [— 3.] | |
| 2a. Bark white or chalky | Paper Birch, Betula alba var. papyrifera. |
| 2b. Bark yellowish | Yellow Birch, Betula lutea. |
| 3a. Shrubs, with leaves 4 cm. long or less [— 4.] | |
| 3b. Shrubs or trees, with leaves 5 cm. long or more [— 5.] | |
| 4a. Twigs glandular-warty | Dwarf Birch, Betula glandulosa. |
| 4b. Twigs not glandular | Swamp Birch, Betula pumila. |
| 5a. Twigs and bark with the odor of wintergreen | Sweet Birch, Betula lenta. |
| 5b. Twigs and bark without odor of wintergreen [— 6.] | |
| 6a. Fruit clusters woody, persistent on the plant for a long time [— 7.] | |
| 6b. Fruit clusters herbaceous, dropping in late autumn [— 9.] | |
| 7a. Leaves rusty or whitish beneath, and pubescent at least on the veins | Speckled Alder, Alnus incana. |
| 7b. Leaves green beneath, and either pubescent or smooth [— 8.] | |
| 8a. Leaves broadest at or below the middle | Mountain Alder, Alnus crispa. |
| 8b. Leaves broadest above the middle | Smooth Alder, Alnus rugosa. |
| 9a. Tree; fruit a cluster of bladder-like sacs each containing a small achene | Ironwood, Ostrya virginiana. |
| 9b. Shrubs; fruit a nut within a close-fitting involucre [— 10.] | |
| 10a. Involucre of 2 broad bracts, almost separate and not much longer than the fruit | Hazel, Corylus americana. |
| 10b. Involucre of united bracts, prolonged into a bristly beak beyond the fruit | Beaked Hazel, Corylus rostrata. |
FAGACEAE, the Beech Family
Trees (or 1 species shrubby), with alternate simple leaves and monoecious flowers, the staminate flowers in catkins, and the pistillate solitary or in small clusters. Fruit a nut (or acorn) enclosed in a cup or bur.
| 1a. Leaves serrate with numerous sharp-pointed teeth [— 2.] | |
| 1b. Leaves serrate, lobed, or entire, but never serrate with sharp-pointed teeth; fruit an acorn; pith 5-angled in the young twigs (Oak) [— 3.] | |
| 2a. Bark gray, smooth; buds 3-4 times longer than wide; nut | Beech, Fagus grandifolia. |
| 2b. Bark rough; buds relatively thicker; nut rounded | Chestnut, Castanea dentata. |
| 3a. Leaves entire, except for a bristle at the tip | Shingle Oak, Quercus imbricaria. |
| 3b. Leaves toothed or lobed, the points bristle-tipped [— 4.] | |
| 3c. Leaves toothed or lobed, the points without bristles [— 10.] | |
| 4a. Leaves entire below the middle, with a few shallow lobes beyond | Black Jack Oak, Quercus marilandica. |
| 4b. Leaves deeply lobed throughout [— 5.] | |
| 5a. Cup of the acorn saucer-shape, covering less than one-third of the acorn [— 6.] | |
| 5b. Cup of the acorn hemispherical or top-shape, covering one-third or more of the acorn [— 8.] | |
| 6a. Length of the lateral leaf-lobes less than one-third the width of the leaf; acorn cup 2-2.5 cm. wide | Red Oak, Quercus rubra. |
| 6b. Length of the lateral leaf-lobes more than one-third the width of the leaf [— 7.] | |
| 7a. Acorn depressed-globose, about 1 cm. in diameter | Pin Oak, Quercus palustris. |
| 7b. Acorn ovoid, 1.5-2 cm. thick | Schneck's Oak, Quercus schneckii. |
| 8a. Leaves pubescent beneath | Black Oak, Quercus velutina. |
| 8b. Leaves glabrous beneath [— 9.] | |
| 9a. Buds glabrous; inner bark of the trunk yellow | Hill's Oak, Quercus ellipsoidalis. |
| 9b. Buds pubescent beyond the middle; inner bark of trunk red | Scarlet Oak, Quercus coccinea. |
| 10a. Leaves deeply pinnately lobed [— 11.] | |
| 10b. Leaves crenate, dentate, or sinuate, not lobed [— 12.] | |
| 11a. Leaf divided nearly to the middle by a pair of deep lateral lobes near the middle of the leaf; acorn more than half covered by the cup | Bur Oak, Quercus macrocarpa. |
| 11b. Leaf without a median pair of deeper lobes; acorn about one-fourth covered by the cup | White Oak, Quercus alba. |
| 12a. Leaves broadest at or near the middle, with numerous (8-13) sharp coarse teeth on each side | Yellow Oak, Quercus muhlenbergii. |
| 12b. Leaves broadest above the middle, with a few shallow, rounded or subacute teeth (7 or less on each side) [— 13.] | |
| 13a. Large tree; leaves densely white-tomentose beneath; acorn on a stalk 3-10 cm. long | Swamp White Oak, Quercus bicolor. |
| 13b. Shrub; leaves thinly white-tomentose beneath; acorn sessile or nearly so | Scrub Oak, Quercus prinoides. |
URTICACEAE, the Nettle Family
Herbs or trees, with small inconspicuous apetalous flowers.
| 1a. Trees or tall shrubs [— 2.] | |
| 1b. Herbs [— 7.] | |
| 2a. Leaves oblong-ovate to lanceolate, serrate [— 3.] | |
| 2b. Leaves broadly ovate to rotund, some of them lobed (Mulberry) [— 6.] | |
| 3a. Leaves thick, coarsely and doubly serrate, broadest near the middle (Elm) [— 4.] | |
| 3b. Leaves thin, simply serrate, broadest distinctly below the middle | Hackberry, Celtis occidentalis. |
| 4a. Some of the branches with flat corky wings; leaves smooth above | Cork Elm, Ulmus racemosa. |
| 4b. Branches without corky wings; leaves more or less rough above [— 5.] | |
| 5a. Petioles and axillary buds glabrous | White Elm, Ulmus americana. |
| 5b. Petioles and axillary buds pubescent with rusty hairs | Slippery Elm, Ulmus fulva. |
| 6a. Leaves rough above | Red Mulberry, Morus rubra. |
| 6b. Leaves smooth above | White Mulberry, Morus alba. |
| 7a. Leaves alternate [— 8.] | |
| 7b. Leaves opposite [— 9.] | |
| 8a. Leaves 2-5 cm. long, stems pubescent | Pellitory, Parietaria pennsylvanica. |
| 8b. Leaves 8-20 cm. long; stem armed with stinging hairs | Wood Nettle, Laportea canadensis. |
| 9a. Twining plant; leaves serrate or cleft | Hop, Humulus lupulus. |
| 9b. Erect plant; leaves palmately compound | Hemp, Cannabis sativa. |
| 9c. Erect plants; leaves not lobed or compound [— 10.] | |
| 10a. Stems armed with stinging hairs [— 11.] | |
| 10b. Stems glabrous or rough, but not with stinging hairs [— 12.] | |
| 11a. Leaves ovate, with a heart-shape base | Stinging Nettle, Urtica dioica. |
| 11b. Leaves lanceolate or ovate-lanceolate, not heart-shape at base | Slender Nettle, Urtica gracilis. |
| 12a. Stems glabrous, pellucid | Clearweed, Pilea pumila. |
| 12b. Stems rough, opaque | False Nettle, Boehmeria cylindrica. |
SANTALACEAE, the Sandalwood Family
Low herbs with alternate entire leaves and terminal clusters of small greenish-white bell-shape flowers without petals in spring and early summer.