KEY TO THE GENERA

(Based on leaves and fruit)

a.—Leaves simple.
b.—Leaves needle-shaped, awl-shaped, or scale-like, usually evergreen; fruit a cone or berry-like.
c.—Leaves in bundles of 2-many; fruit a cone.
Leaves in bundles of 2-5, evergreen
Pinus, p. [13].
Leaves in clusters of 8-many on short spur-like branchlets, deciduous in autumn
Larix, p. [13].
c.—Leaves not in bundles, solitary.
d.—Leaves alternate or whorled.
Leaves 4-angled, harsh, needle-shaped
Picea, p. [13].
Leaves flat, whitened beneath, ½-1¼ inches long, sessile, aromatic; cones 2-4 inches long with deciduous scales; bark of twigs smooth, and on old trunks with raised resin-filled blisters
Abies, p. [14].
Leaves two-fifths to one-half inch long, short-petioled, flat and whitened beneath; cones about ¾ inch long with persistent scales; bark of twigs rough
Tsuga, p. [14].
d.—Leaves opposite.
Leaves scale-like, decurrent on the stem, all of one kind; twigs flattened; fruit a small elongated cone with 8-12 over-lapping scales
Thuja, p. [14].
Leaves of two kinds, either scale-like or awl-shaped, not decurrent on the stem; twigs nearly terete; fruit a bluish, berry-like strobile
Juniperus, p. [14].
b.—Leaves flat and broad, usually deciduous.
c.—Leaves alternate or clustered.
d.—Leaves without lobes.
e.—Leaves with margins entire or slightly undulate.
f.—Leaves deciduous.
Leaves 2-5 inches long, oval; fruit an ovoid, blue berry-like drupe, borne 1-3 in a drooping cluster
Nyssa, p. [25].
Leaves 2-5 inches long, ovate; fruit a spherical, blue berry-like drupe, borne many in an upright cyme, (Cornus alternifolia)
Cornus, p. [25].
Leaves 4-6 inches long, oval; fruit an edible berry ¾-1¼ inches in diameter
Diospyros, p. [26].
Leaves 4-12 inches long, obovate-lanceolate; fruit banana-like, 3-5 inches long, with many flattened seeds in the yellow flesh
Asimina, p. [20].
Leaves 6-24 inches long, ovate-obovate; fruit a cone-like or cucumber-like cylindrical mass 2-4 inches long
Magnolia, p. [20].
Leaves 3-5 inches long, heart-shaped; fruit a pod 2-3 inches long
Cercis, p. [23].
Leaves 4-6 inches long, oblong-lanceolate; fruit an acorn (Quercus imbricaria)
Quercus, p. [17].
f.—Leaves evergreen.
Leaves 3-4 inches long; fruit many dry spherical capsules in a corymb
Kalmia, p. [26].
Leaves 4-11 inches long, evergreen; fruit an oblong, dry capsule, several in umbel-like clusters
Rhododendron, p. [26].
e.—Leaves with margins toothed.
f.—Branches armed with stiff, sharp thorns.
Leaves 1-3 inches long, serrate or doubly serrate; fruit a small pome
Crataegus, p. [22].
f.—Branches not armed with thorns.
g.—Base of leaf decidedly oblique.
Leaf-blade broad, heart-shaped, serrate; fruit a spherical woody drupe on stalks attached to an oblong bract
Tilia, p. [25].
Leaf-blade oval, doubly-serrate, primary veins straight; fruit an oval samara
Ulmus, p. 19.
Leaves 2-4 inches long, serrate; fruit a small sweet purple drupe
Celtis, p. [19].
g.—Base of leaf nearly symmetrical.
h.—Teeth coarse, 2-5 to the inch.
Leaves smooth, oval, 3-5 inches long; fruit a small bur with weak prickles and 3-faced nuts ½-¾ inch long
Fagus, p. [17].
Leaves 6-8 inches long; fruit a bur with stiff prickles and 1-3 rounded, brown nuts
Castanea, p. [17].
Leaves 2-4 inches long, broadly ovate to sub-orbicular; fruit a small capsule falling in spring
Populus, p. [15].
Leaves 4-8 inches long, lanceolate to obovate; fruit an acorn
Quercus, p. [17].
Leaves wavy-toothed with sharp spines, evergreen; fruit a small red drupe
Ilex, p. [24].
Leaves 4-6 inches long, oval; fruit a short woody pod with black seeds
Hamamelis, p. [21].
h.—Teeth fine, 6-many to the inch.
i.—Leaves not doubly serrate.
Leaves 1½-2 inches long, nearly as broad, tremulous on long petioles; fruit a small capsule. (P. tremuloides)
Populus, p. [15].
Leaves 2-6 inches long, often narrow; twigs easily separated at the joints; fruit a small capsule
Salix, p. [14].
Leaves 5-7 inches long, 1½-2½ inches wide, very smooth; bark acid; fruit a 5-valved capsule borne in clusters
Oxydendrum, p. [26].
Leaves 2-5 inches long, ovate to lanceolate; bark often bitter; fruit a drupe
Prunus, p. 22.
Leaves 3-4 inches long; fruit a red berry-like pome in clusters
Amelanchier, p. [22].
Leaves 3-5 inches long, nearly as wide, often heart-shaped, sometimes 2-5-lobed; fruit oblong, about 1 inch long, composed of many small drupes
Morus, p. [19].
Leaves 3-4 inches long, often doubly serrate or lobed on sterile shoots; fruit a greenish-yellow pome about 1 inch in diameter
Pyrus, p. [21].
Leaves 4-6 inches long, ovate-lanceolate; fruit 1-2 inches long, dry, 4-winged
Halesia, p. [26].
Leaves 4-5 inches long, ovate; fruit scarlet berry-like drupes on short stems and scattered along the branches (Ilex monticola)
Ilex, p. [24].
Leaves 2-5 inches long; fruit cone-like, containing many dry scales (B. lenta)
Betula, p. [16].
i.—Leaves doubly serrate.
Leaves 2-4 inches long, thin; fruit a small nut enclosed in a halberd-shaped leaf-like involucre; trunk smooth and fluted
Carpinus, p. [16].
Leaves 3-5 inches long; fruit hop-like, composed of several inflated bracts overlapping and each containing a flat seed; bark brown with loose scales
Ostrya, p. [16].
Leaves 2-4 inches long; bark peeling off in papery scales; fruit oblong or ovate, 1-2 inches long, composed of numerous 3-lobed scales, bearing winged nuts
Betula, p. [16].
Leaves 1-3 inches long, sometimes serrate or lobed; twigs armed with stiff thorns; fruit a hard pome
Crataegus, p. [22].
Leaves 3-4 inches long, often serrate or lobed; fruit a sour yellowish pome about 1 inch in diameter
Pyrus, p. [21].
d.—Leaves lobed.
e.—Margins of lobes entire.
Leaves oval often without lobes or with 2-3 lobes, smooth, aromatic; fruit a dark blue drupe borne on a thickened red stem
Sassafras, p. [21].
Leaves broadly ovate, with truncate apex, 2 apical and 2-4 basal lobes; fruit a cone-like aggregate of dry, lance-shaped carpels
Liriodendron, p. [20].
Leaves variously lobed, some with bristle-tipped teeth; fruit an acorn
Quercus, p. [17].
e.—Margins of lobes not entire.
Leaves thick, glossy, star-shaped, with fine pointed serrate lobes; fruit a pendulous spiny spherical head about 1 inch thick, composed of numerous capsules
Liquidambar, p. [21].
Leaves oval, pointed, often without lobes, thin, margins serrate or doubly serrate; fruit a yellowish pome 1-1½ inches thick
Pyrus, p. [21].
Leaves oval, pointed, often without lobes, thin, margins serrate or doubly serrate; fruit a pome about two-fifths of an inch thick, often red; twigs armed with thorns
Crataegus, p. [22].
Leaves often broadly ovate and not lobed, sometimes with 2-5 lobes, serrate; fruit oblong, about 1 inch long, an aggregate of many small dark purple drupes
Morus, p. [19].
Leaves nearly round in outline, 3-5 lobed, coarse sinuate-toothed; fruit a round pendulous head 1 inch thick; composed of many hairy achenes
Platanus, p. [21].
c.—Leaves opposite.
d.—Leaf margins entire or slightly undulate.
Leaves 3-5 inches long, ovate; fruit a bright red ovoid drupe, two-fifths inch long in small bunches
Cornus, p. [25].
Leaves 4-8 inches long, ovate; fruit a dark blue ovoid drupe, ¾ of an inch long, in drooping, loose clusters
Chionanthus, p. [27].
d.—Leaf margins not entire.
Leaves 3-5 lobed, finely or coarsely toothed, fruit a drooping samara
Acer, p. [24].
Leaves not lobed, 1-3 inches long, oval, finely toothed; fruit a dark blue drupe borne in clusters
Viburnum, p. [27].
a.—Leaves compound.
b.—Leaves alternate.
c.—Margins of leaflets entire.
Leaves pinnate, 8-14 inches long; fruit a pod 2-4 inches long; limbs bearing short spines in pairs at the nodes
Robinia, p. [23].
Leaves 3-foliate; fruit a samara, winged all around, in drooping clusters
Ptelea, p. [23].
Leaves pinnate with 9-21 leaflets; fruit small, red or white dry drupes in dense upright or loose drooping clusters
Rhus, p. [23].
c.—Margins of leaflets not entire.
Leaves pinnate with 11-23 serrate leaflets; fruit a large sculptured nut
Juglans, p. [15].
Leaves odd-pinnate, with 3-11 leaflets; fruit a smooth or angled nut
Carya, p. [15].
Leaves odd-pinnate, with 13-17 lance-shaped leaflets; fruit a small red acid pome, borne many in a flat-topped cluster. (Pyrus Americana)
Pyrus, p. [21].
Leaves doubly compound with many ovate serrate leaflets; fruit a small ovoid black berry in large branching clusters; twigs and trunk armed with sharp spines
Aralia, p. [25].
b.—Leaves opposite.
c.—Leaves pinnate, fruit a samara.
Leaflets, 3-5, samaras paired
Acer, p. [24].
Leaflets, 5-11, samaras, not paired
Fraxinus, p. [26].
c.—Leaves digitate, fruit a globular capsule containing large brown nuts
Aesculus, p. [25].