Method of Using the Key.

First read all the statements following the stars (*) at the beginning of the Key; decide which one of the statements best suits the specimen you have. At the end of the chosen one there is a letter in parenthesis ( ). Somewhere below, this letter is used two or more times. Read carefully all the statements following this letter; at the end of the one which most nearly states the facts about your specimen, you will again be directed by a letter to another part of the Key. Continue this process till, instead of a letter, there is a number and name. The name is that of the genus, and forms the first part of the scientific name of the plant. Turn to the descriptive part of the book, where this number, in regular order, is found. Here descriptions of the species of the genus are given. If there are many species, another Key will lead to the species. While the illustrations are intended to represent characteristic specimens, too much dependence must not be placed upon them; the leaves even of the same plant vary considerably, and the different varieties, especially of a cultivated plant, vary widely. Read the whole description before deciding.

The fractions beside the figures indicate the scale of the drawing as compared with the natural size of the part: 1/1 indicates natural size; 2/1, that the drawing is twice the length of the object; ¼, that the drawing is one fourth the length of the object, etc.

In the description of leaves the dimensions given refer to the blade.

KEY TO THE GENERA OF TREES.

* Leaves narrow linear, needle, scale or awl shaped, usually but not always evergreen. (GG.) [page 60].
* Leaves broad, flat, usually deciduous, occasionally evergreen, rarely over 5 times as long as wide. (A.)
A. Leaves alternate,[1] simple. (B.)
A. Leaves alternate, compound. (m.) [page 57].
A. Leaves opposite or whorled on the stem. (u.) [page 58].
B. Leaves with a midrib, netted-veined. (C.)
B. Leaves without a midrib, parallel-veined109. [Salisburia.]
C. With radiating ribs, and including those which have the lower ribs longer and more branching than those above them. (f.) [page 56].
C. With distinct and definite feather-veining. (D.)
D. Margin entire, or so nearly so as to appear entire, sometimes slightly angulated but not lobed. (V.)
D. Once or twice serrate or crenate or wavy-edged, but not lobed. (E.)
D. Distinctly lobed. (S.) (If the notches are over 10 on a side, look under E.)
E. Straight-veined. (M.)
E. Not distinctly and evenly straight-veined. (F.)
F. Leaves evergreen with either revolute or spiny-tipped margins18. [Ilex.]
F. Leaves evergreen, lanceolate-oblong, minutely serrate; flowers white, 4 in. in diameter8. [Gordonia.]
F. Leaves deciduous. (G.)
G. Fruit with fleshy and often edible pulp. (K.)
G. Fruit a dry and more or less rounded pod. (H.)
G. Fruit and flowers in dry catkins; leaves, in most species, 3 or more times as long as wide, finely serrate to entire, with free stipules, in many species remaining on the young twigs, in others shown by a rounded scar on the sides of the stem; wood soft; the Willows91. [Salix.]
G. Fruit dry akenes with silky pappus, in small heads; whole plant whitened with scurf; leaves broadened and coarsely notched near tip; a broad spreading bush49. [Baccharis.]
H. Flowers conspicuous, 1 in. or more in size, white. (J.)
H. Flowers quite small. (I.)
I. Flowers and fruit in large panicles; leaves elongated, peach-like in shape, sour50. [Oxydendrum.]
I. Flowers in terminal, erect racemes; fruit small, three-celled pods; leaves oval, 3-7 in. long, pointed, thin, finely serrate; plant hardly a tree53. [Clethra.]
I. Fruit rounded, small, with calyx adhering to the lower part, one-seeded, in clusters of 3-many; leaves 1-3 in. long.56. [Styrax.]
I. Fruit hairy, in long, hanging panicles, tipped with long, persistent style, one-seeded57. [Pterostyrax.]
J. Flowers bell-shaped, 1 in. long; leaves widest below the middle; fruit winged pods58. [Halesia.]
J. Flowers spreading, 2 in. broad; leaves about twice as long as wide, widest near the center7. [Stuartia.]
J. Flowers spreading, 3 in. broad; leaves about 3 times as long as wide, widest near tip8. [Gordonia.]
K. Fruit a plum-like drupe with a single bony stone; plant sometimes thorny36. [Prunus.]
K. Fruit berry-like, ending in a conspicuous spreading calyx; plant generally quite thorny38. [Cratægus.]
K. Fruit berry-like, black when ripe, small, without calyx, with usually 3 cartilaginous coated seeds20. [Rhamnus.]
K. Fruit berry-like, red when ripe, small, without calyx, with usually 4-6 hard-coated, grooved nutlets 18. [Ilex.]
K. Fruit a small or large apple-like pome, with the seeds in horny cells. (L.)
L. Fruit about ½ in. in diameter, sweet, in drooping racemes39. [Amelanchier.]
L. Fruit either sour or much larger, and not in elongated racemes37. [Pyrus.]
M. Leaves harsh to the touch; somewhat oblique at base; quite distinctly two-ranked; large trees74. [Ulmus.]
M. Leaves decidedly oblique at base; margin wavy; small tree, usually a shrub40. [Hamamelis.]
M. Fruit berry-like, ending in a conspicuous spreading calyx; plant generally quite thorny38. [Cratægus.]
M. Leaves not regularly oblique at base; plant not thorny. (N.)
N. Leaves thin and light, not harsh to the touch; spray light; bark smooth, in two species somewhat rough on the trunk. (Q.)
N. Leaves thick; edge wavy, almost lobed; fruit an acorn. 88. [Quercus.]
N. Leaves broad for the length, generally doubly serrate or wavy and serrate; shrubs, rarely tall enough for trees. (P.)
N. Not included in the above. (O.)
O. Leaves 3 or more times as long as wide, widest near the center; fruit a round, prickly bur with 1-3 horny-coated nuts89. [Castanea.]
O. Leaves widest near the sharply serrate tip, narrow and entire near the base; fruit small pods in terminal racemes; small tree or shrub53. [Clethra.]
O. Leaves widest near the base, usually small; bark scaling off like the Buttonwood; fruit axillary, solitary, small (¼ in.) roundish, dry drupes. A cultivated species, has rather large leaves, widest near the center75. [Planera.]
P. Fruit an open oval woody catkin or cone, remaining on the plant through the winter84. [Alnus.]
P. Fruit a rounded stony nut, in green leafy edged bracts; shrubs or small trees85. [Corylus.]
Q. Usually aromatic; bark dotted on the spray and with horizontal marks on the trunk, peeling off in thin, often papery layers83. [Betula.]
Q. Bark not peeling off in thin layers. (R.)
R. Leaf-buds long and slender; fruit a small prickly bur with two triangular, horny-coated nuts; large trees 90. [Fagus.]
R. Fruit an elongated catkin with large leaf-like bracts; bark close, gray, on a grooved trunk87. [Carpinus.]
R. Fruit a hop-like catkin; bark brownish, finely furrowed 86. [Ostrya.]
S. Plant more or less thorny; shrub or small tree; fruit rounded berries ending in persistent calyx-lobes38. [Cratægus.]
S. Plant not thorny. (T.)
T. Leaf deeply pinnatifid, usually with the basal lobes completely separated; cultivated37. [Pyrus.]
T. End of leaf as though cut off; sides with one large lobe; margin entire; large tree2. [Liriodendron.]
T. Lower leaves three-lobed, heart-shaped at base, upper merely ovate, margin entire; small tree or shrub 66. [Clerodendron.]
T. Not as above; leaves usually many-lobed. (U.)
U. Leaves thin; bark of trunk peeling off in thin horizontal strips83. [Betula.]
U. Leaves thin; leaf-buds long, slender, sharp-pointed; bark smooth, not peeling; cultivated90. [Fagus.]
U. Leaves thickish; bark roughish; fruit an oval woody cone, remaining on through the year84. [Alnus.]
U. Leaves thick; fruit an acorn88. [Quercus.]
V. Leaves evergreen, small, 2-3 in. long, thick, with revolute margins; fruit an acorn88. [Quercus.]
V. Leaves evergreen, oval to lance-oval, usually large; small trees, almost shrubs. (d.) page 56.
V. Leaves deciduous (some are evergreen in the Southern States). (W.)
W. Plant more or less spiny. (c.)
W. Plant not at all spiny. (X.)
X. Leaf-blade thin, long, pointed, with curved parallel veins or ribs45. [Cornus.]
X. Leaf-blade thin, circular or broadly oval in outline, with blunt, almost rounded apex; veins not regularly parallel27. [Rhus.]
X. Leaf quite elongated, 5 or more times as long as wide. (b.)
X. Leaves with none of the above peculiarities. (Y.)
Y. Deciduous bud-scales (stipules), leaving a scar or mark completely around the stem at the base of the leaves.1. [Magnolia.]
Y. Leaves covered on one or both sides with silvery scales71. [Elæagnus.]
Y. No such ring around the stem, or silvery scales on the leaves. (Z.)
Z. Leaves distinctly straight-veined, thin90. [Fagus.]
Z. Leaves thick, obtuse; fruit an acorn88. [Quercus.]
Z. Leaves 6 in. or more long; crushed leaves with a rank, fetid odor5. [Asimina.]
Z. Leaves 3-5 in. long; twigs and leaves very spicy; shrub rather than tree70. [Lindera.]
Z. Leaves about 2 in. long, oval, on twigs which have ridges extending down from the sides of the leafstalk; small tree, almost a shrub, with beautiful flowers 43. [Lagerstroemia.]
Z. Leaves not as above. (a.)
a. Fruit a large (½-1½ in.) rounded pulpy berry with a heavy calyx at the base55. [Diospyros.]
a. Fruit small (¼ in.), fleshy, drupe-like, with a striate stone; limbs branching horizontally, often descending46. [Nyssa.]
a. Fruit a black, juicy berry (1/3-½ in.), with about 3 seeds20. [Rhamnus.]
a. Fruit an ovoid dry drupe (½ in.); leaves sweet-tasting59. [Symplocos.]
a. Fruit an apple-like pome (Quince)37. [Pyrus.]
b. Wood soft; both kinds of flowers in catkins in spring; with either stipules or stipular sears91. [Salix.]
b. Wood hard; leaves thick; fruit an acorn88. [Quercus.]
c. Fruit a 2-4-seeded small berry; juice not milky20. [Rhamnus.]
c. Fruit large, orange-like in size and color when ripe; juice milky77. [Maclura.]
c. Fruit small, black when ripe, cherry-like; juice milky54. [Bumelia.]
d. Aromatic; berries dark blue on red stalks68. [Persea.]
d. Not aromatic; leaves nearly 1 ft. long; flowers large and solitary.1. [Magnolia.]
d. Not aromatic; leaves 1-4 in. long; flowers very small; fruit small dark-colored berries, with 2-4 seeds20. [Rhamnus.]
d. Not aromatic; flowers large, in showy clusters. (e.)
e. Leaves 5 in. or more long52. [Rhododendron.]
e. Leaves less than 4 in. long51. [Kalmia.]
f. Leaves decidedly aromatic, usually somewhat irregularly lobed, margin entire, base tapering69. [Sassafras.]
f. Leaves usually deltoid, sometimes heart-shaped with serrate margin and gummy buds, rarely palmately lobed. All have either the petiole flattened sidewise, the leaf-blade densely silvery-white beneath, or gummy aromatic buds92. [Populus.]
f. Leaves broadly heart-shaped; margin entire; small tree with abundance of red flowers in early spring; fruit a pea-like pod.32. [Cercis.]
f. Leaves not as above given. (g.)
g. Leaves broadly heart-shaped, with a serrate margin and a petiole about as long as the blade, sometimes longer; base of leaf not oblique4. [Idesia.]
g. Leaves broadly heart-shaped, those on the suckers much lobed; base not oblique; margin serrate; juice milky; bark very tough. (l.)
g. Leaves broadly heart-shaped, with an oblique base; margin regularly serrate; juice not milky11. [Tilia.]
g. Leaves slightly if at all heart-shaped at base, usually somewhat oblique, with neither milky juice nor lobes. (j.)
g. Leaves decidedly and quite regularly lobed. (h.)
h. Leaves with 3-5 large lobes, the margin entire or slightly angulated.10. [Sterculia.]
h. Leaves star-shaped, with 5-9 pointed, serrate lobes. (i.)
h. Leaves large, irregularly margined; leaf-stem covering the bud; large tree80. [Platanus.]
h. Plant quite thorny; fruit berry-like, ending in a conspicuous spreading calyx; small trees or shrubs with apple-like blossoms.38. [Cratægus.]
h. Leaves with a tapering base; small tree, almost a shrub, with large Hollyhock-like flowers; plant not thorny9. [Hibiscus.]
i. Large tree, with fruit 1 in. in diameter, dry, rough, hanging on a long stem41. [Liquidambar.]
i. Small tree with few branches and the trunk usually quite prickly; fruit berry-like in large clusters44. [Aralia.]
j. Fruit small berries, with 3 flattened seeds, in clusters in the axils of the leaves, which are decidedly 3-ribbed from the base21. [Hovenia.]
j. Fruit small drupes, with 1 seed, either solitary or in pairs in the axils of the leaves. (k.)
k. Plant without prickles; leaves decidedly oblique at base76. [Celtis.]
k. Plant with prickles; leaves narrow, decidedly 3-ribbed, and 2-ranked on green twigs22. [Zizyphus.]
l. Fruit not very edible; leaves rough above, very hairy below, on some of the twigs opposite79. [Broussonetia.]
l. Fruit edible; leaves not very hairy, never opposite78. [Morus.]
m. Leaves of 3 entire-edged leaflets; fruit a pea-like pod28. [Laburnum.]
m. Leaves of 3 quite regularly serrate, transparent-dotted leaflets13. [Ptelea.]
m. Leaves once or twice pinnate; the leaflets entire. (s.)
m. Leaves once or twice pinnate; the leaflets with margins more or less serrate or notched. (n.)
n. Leaves irregularly once to twice, in one case three times, pinnate. (r.)
n. Leaves regularly once pinnate. (o.)
o. Leaves less than 1 ft. long, on a small, quite prickly plant; fruit very small pods (¼ in. long)12. [Xanthoxylum.]
o. Leaves less than 1 ft. long; leaflets 3 in. or less long; fruit bright-colored, berry-like pomes in clusters, persistent through the autumn; plant not thorny; branches not heavy-tipped.37. [Pyrus.]
o. Leaves usually larger on the small tree or almost a shrub; juice in most cases milky; branches heavy-tipped27. [Rhus.]
o. Leaves 1-2 ft. long; leaflets 3 in. or more long; fruit a bony nut with green fleshy coat; large trees. (q.)
o. Leaves very large, 2 ft. or more long on the rapid-growing branches; branches heavy-tipped; odor of bruised leaves quite strong; leaflets 15 or more in number; large trees; juice not milky. (p.)
p. Leaflets with 1-3 glandular notches at the base17. [Ailanthus.]
p. Leaflets entire at base, but very slightly serrate near the tip16. [Cedrela.]
q. Coat of fruit more or less dehiscent into 4 valves; nut smoothish; leaflets, except in one species, not over 11 in number, usually 5-782. [Carya.]
q. Coat of fruit not regularly dehiscent; nut, in the wild species, rough-coated; leaflets, except in a cultivated species, over 11 in number81. [Juglans.]
r. Leaves quite regularly twice odd-pinnate; leaflets about 1 in. long; juice not milky; fruit rounded berries in large clusters; plant not prickly; branchlets not heavy-tipped15. [Melia.]
r. Leaves once to twice irregularly odd-pinnate; the leaflets very irregularly and coarsely toothed; a small, round-headed tree with bladdery pods24. [Koelreuteria.]
r. Leaves irregularly about twice odd-pinnate; the leaflets lanceolate; quite a low plant with few heavy-tipped branches; plant without prickles27. [Rhus.]
r. Leaves 2 (sometimes 3) times odd-pinnate; tree-stem with prickles; small tree or shrub, with few branches44. [Aralia.]
r. Leaves once to twice abruptly pinnate; large tree with slender-tipped branches, usually very thorny34. [Gleditschia.]
s. Leaves very large (2 ft. or more long), about twice abruptly pinnate; leaflets broad and often 2 in. long; branches blunt; no thorns33. [Gymnocladus.]
s. Leaves and leaflets much smaller, leaves quite irregularly once or twice abruptly pinnate; branches slender-tipped; large tree, usually very thorny34. [Gleditschia.]
s. Leaves twice abruptly pinnate; leaflets over 400 in number, with midrib near the upper edge35. [Albizzia.]
s. Leaves regularly once pinnate, not over 2 ft. long. (t.)
t. Leaves abruptly pinnate, not over 5 in. long; leaflets 8-12, small, mucronate-pointed29. [Caragana.]
t. Leaves odd-pinnate; shrub or small tree, with few, heavy-tipped branches; no spines or prickles27. [Rhus.]
t. Leaves odd-pinnate; leaflets large (3-5 in. long), not usually over 11 in number; round-topped tree30. [Cladrastis.]
t. Leaves odd-pinnate; leaflets less than 3 in. long, frequently 11-21 in number; often with spines at the bases of the leaves in the place of stipules12. [Xanthoxylum]
or 31. [Robinia.]
u. Leaves palmately compound. (CC.)
u. Leaves pinnately compound. (BB.)
u. Leaves simple, evergreen, sessile, in whorls around the stem, which they completely cover(98a. [Araucaria.])
u. Leaves simple, opposite, evergreen, entire, over 2 in. long61. [Osmanthus.]
u. Leaves simple, opposite, evergreen, entire, under 1 in. long73. [Buxus.]
u. Leaves simple, deciduous. (v.)
v. Branches ending in thorns; small trees, or shrubs. (AA.)
v. Plants not thorny. (w.)
w. Leaves palmately lobed (one variety, rarely cultivated, lacks lobes, but is heart-shaped with a serrate margin), the lobes over 3 in number, or with notches or serrations; fruit dry, winged25. [Acer.]
w. Lower leaves palmately 3-lobed, and heart-shaped at base, upper ones ovate, all with entire margin; fruit with juicy pulp covering the 4 seeds66. [Clerodendron.]
w. Leaves palmately lobed; fruit small, one-seeded, berry-like drupes in large clusters, with flattened stones, or large rounded clusters of flowers without stamens or pistils; shrubs rather than trees47. [Viburnum.]
w. Leaves heart-shaped, entire or slightly angulated; not lobed. (DD.)
w. Leaves irregularly serrate, somewhat straight-veined; fruit single-winged; large cultivated tree60. [Fraxinus.]
w. Leaves neither heart-shaped nor lobed; small trees, almost shrubs. (x.)
x. Leaves entire. (z.)
x. Leaves serrate or dentate, ovate or oval. (y.)
y. Fruit rounded drupes in large clusters, with single flattened stones47. [Viburnum.]
y. Fruit lobed pods, which burst open in the autumn; branchlets somewhat 4-sided19. [Euonymus.]
z. Leaves small, lanceolate; flowers and fruit large and beautiful42. [Punica.]
z. Leaves broad, thin, with curved parallel veins or ribs.45. [Cornus.]
z. Leaves large, broad, oval, without either curved or straight parallel ribs63. [Chionanthus.]
AA. Leaves entire and covered on both sides with silvery, peltate scales72. [Shepherdia.]
AA. Leaves ovate, small, minutely serrate20. [Rhamnus.]
BB. Leaves large, 18 in. or more long; leaflets 11 or more, very finely serrated14. [Phellodendron.]
BB. Leaves smaller; leaflets entire or quite evenly toothed, usually over 5 in number60. [Fraxinus.]
BB. Leaflets coarsely and quite irregularly toothed, 3-5 (rarely 7) in number26. [Negundo.]
CC. Leaflets slender-lanceolate, almost entire; shrub or small tree, 5-10 ft. high67. [Vitex.]
CC. Leaflets broader and serrate; usually large trees.23. [Æsculus.]
DD. Leaves with radiating ribs. (FF.)
DD. Leaves with feather-veining. (EE.)
EE. Leaves 2-6 in. long; flowers small, in large, dense, terminal clusters62. [Syringa.]
EE. Leaves 1-4 in. long; flowers in pairs48. [Lonicera.]
FF. Leaves large, 6 in. or more long; two almost hidden buds, one above the other, in the axils of the leaves on the rapid-growing branches; flowers large, purple, blooming in early spring; fruit rounded pods64. [Paulownia.]
FF. Leaves large, 6 in. or more long; flowers large, white, blooming in June; fruit long pods65. [Catalpa.]
FF. Leaves 2-4 in. long, with red stems3. [Cercidiphyllum.]
GG. Leaves scattered singly over the stem, not in bundles or clusters. (JJ.)
GG. Leaves in large or small clusters. (HH.)
HH. Clusters in whorls of many leaves around the stem like an umbrella100. [Sciadopitys.]
HH. Leaves clustered in bundles of 2-693. [Pinus.]
HH. Leaves clustered in bundles of over 8. (II.)
II. Leaves deciduous, soft97. [Larix.]
II. Leaves evergreen, rigid98. [Cedrus.]
JJ. Leaves hardly evergreen; spray quite slender. (ZZ.)
JJ. Leaves fully evergreen. (KK.)
KK. Leaves awl or scale shaped, and mainly appressed to the stem. (WW.)
KK. Leaves linear or needle shaped, and decidedly spreading from the stem, though sometimes with a decurrent base. (LL.)
LL. Leaves narrowed to a distinct though short stem. (RR.)
LL. Leaves sessile; if narrowed, not so abruptly as to form a petiole. (MM.)
MM. Leaves opposite or whorled on the stem. (PP.)
MM. Leaves rather spirally arranged around the stem, not just opposite. (NN.)
NN. Leaves linear to lanceolate, flattened, spreading quite squarely from the stem. (OO.)
NN. Leaves not flattened but 4-sided, curved, gradually enlarging from the tips to the bases, which are decurrent, and on the young twigs completely cover the stem; cones rounded; the scales not lapping105. [Cryptomeria.]
OO. Leaves about linear in form, of nearly the same width throughout, and usually fastened to the cylindrical stem by a distinct disk-like base; cones erect; scales lapping.96. [Abies.]
OO. Leaves about 2 in. long and gradually widening from the acute tips to the broad (1/8 in.) bases, which are decurrent on the stem99. [Cunninghamia.]
OO. Leaves ½-1 in. long, sharp-pointed, very flat, two-ranked, somewhat lanceolate in form; base narrowed almost to a petiole102. [Sequoia.]
PP. Leaves not decurrent, usually in whorls of three around the stem, sometimes opposite, acute-pointed; fruit small (1/8 in.), rounded, dark-colored berries106. [Juniperus.]
PP. Leaves decurrent on the stem, less than ½ in. long. (QQ.)
QQ. Fruit small, globular cones; the scales not lapping104. [Chamæcyparis.]
QQ. Fruit small, elongated cones of few, lapping scales103. [Thuya.]
RR. Leaves usually but little flattened, but jointed to a short, brown petiole which is attached to a somewhat grooved twig; cones pendent, of lapping scales94. [Picea.]
RR. Leaves decidedly flattened, not jointed, but narrowed to a petiole which is usually green or greenish in color. (SS.)
SS. Leaves rounded or obtuse at the tip, distinctly two-ranked, usually less than 1 in. long; cones oval, 1 in. or less long, of lapping scales95. [Tsuga.]
SS. Leaves acute at the tip; fruit (found only on a portion of the plants, as the flowers are dioecious) drupe-like, with a single nut-like seed. (TT.)
TT. Leaves not two-ranked, over 2 in. long108. [Podocarpus.]
TT. Leaves quite regularly two-ranked. (UU.)
UU. Leaves marked by two longitudinal lines; bruised or burned leaves with a very disagreeable odor(107a. [Torreya.])
UU. Leaves with the midrib forming a distinct ridge, odor not disagreeable. (VV.)
VV. Leaves usually less than an inch long107. [Taxus.]
VV. Leaves usually more than an inch long(107b. [Cephalotaxus.])
WW. Spray decidedly two-ranked, fan-like. (YY.)
WW. Spray branching in an irregular way, not two-ranked. (XX.)
XX. Fruit a purplish berry; bark shreddy106. [Juniperus.]
XX. Fruit a cone of thick, pointed, not lapping scales102. [Sequoia.]
YY. Cones elongated, of lapping scales103. [Thuya.]
YY. Cones globular, of peltate, valvate scales104. [Chamæcyparis.]
ZZ. Leaves very broad at base, half clasping the stem and rapidly narrowed to an acute tip; hardly at all spreading from the thread-like twigs; flowers pinkish, in spike-like clusters6. [Tamarix.]
ZZ. Leaves more elongated, quite even in width, not clasping the stem101. [Taxodium.]

[1] Look on the elongated branches for the arrangement of the leaves; they are too closely clustered on the short side shoots. See [page 18].

CLASS I. ANGIOSPÉRMÆ.

Plants with a pistil consisting of a closed ovary, which contains the ovules and forms the fruit.

Order I. MAGNOLIACEÆ. (Magnolia Family.)