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SUMMER KEY TO THE GENERA A

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a. Leaves simple.
b. Leaves needle-shaped, awl-shaped, strap-shaped or scale-like.
c. Leaves in clusters of 2-many.
d. Leaves in clusters of 2-5, sheathed, persistent for several years. PINUS, p. 4.
dd. Leaves in fascicles of 8-many, on short, lateral branchlets, deciduous in autumn. LARIX, p. 17.
cc. Leaves solitary, not clustered.
d. Leaves opposite.
e. Twigs flattened; leaves all of one kind, scale-like, decurrent on the stem; fruit a small, pale brown cone. THUJA, p. 31.
ee. Twigs essentially terete; leaves of two kinds, either scale-like, or else awl-shaped, often both kinds on the same branch, not decurrent on the stem; fruit berry-like, bluish. JUNIPERUS, p. 33.
dd. Leaves alternate or spirally-whorled.
e. Leaves flattened, soft to the touch.
f. Leaves 1/2-1-1/4 inches long, sessile, aromatic; cones 2-4 inches long; bark of trunk with raised blisters containing resin. ABIES, p. 27.
ff. Leaves seldom over 1/2 inch long, short-petioled, not aromatic; cones about 3/4 inch long; bark of trunk without raised blisters. TSUGA, p. 29.
ee. Leaves 4-sided, harsh to the touch. PICEA, p. 18.
bb. Leaves broad and flat.
c. Leaves alternate or clustered, never opposite nor whorled.
d. Margin of leaves entire or only slightly undulate.
e. Leaves heart-shaped or rounded; fruit a legume. CERCIS, p. 167.
ee. Leaves oval, ovate or obovate; fruit not a legume.
f. Branches armed with stout, straight spines; fruit large, orange-like. MACLURA, p. 133.
ff. Branches without spines; fruit small, not orange-like.
g. Fruit an acorn. QUERCUS, p. 96.
gg. Fruit a drupe or berry.
h. Twigs spicy-aromatic when bruised; leaves of many shapes on the same branch. SASSAFRAS, p. 139.
hh. Twigs not spicy-aromatic; leaves not of many shapes on the same branch.
i. Leaves thick, abruptly pointed, very lustrous above, not clustered at the ends of the branches. NYSSA, p. 209.
ii. Leaves thin, long-pointed, not lustrous above, clustered at the ends of the branches. CORNUS, p. 202.
dd. Margin of leaves serrate, toothed or lobed.
e. Margin of leaves serrate to toothed.
f. Branches armed with stiff, sharp thorns. CRATAEGUS, p. 151.
ff. Branches not armed.
g. Base of leaves decidedly oblique.
h. Leaf-blades about as long as they are broad, heart-shaped. TILIA, p. 201.
hh. Leaf-blades 1-1/2 - 2 times as long as they are broad, oval to ovate.
i. Leaves thin, coarsely but singly serrate; fruit a globular drupe, ripe in autumn. CELTIS, p. 131.
ii; Leaves thick, coarsely and doubly serrate; fruit a samara, ripe in spring. ULMUS, p. 122.
gg. Base of leaves essentially symmetrical.
h. Teeth coarse, 2-5 per inch of margin.
i. Leaves very glabrous both sides; fruit a prickly bur.
j. Leaves 3-5 inches long, very lustrous beneath; bark close, smooth, steel-gray. FAGUS, p. 93.
jj. Leaves 6-8 inches long, not lustrous beneath; bark fissured, brownish. CASTANEA, p. 95.
ii. Leaves pubescent or white-tomentose, at least beneath; fruit not a prickly bur.
j. Leaves 2-4 inches long, broadly ovate to suborbicular; fruit a very small capsule, falling in spring. POPULUS, p. 44.
jj. Leaves 4-7 inches long, oblong-lanceolate to obovate; fruit an acorn, falling in autumn. QUERCUS, p. 96.
hh. Teeth fine, 6-many per inch of margin.
i. Leaf-petioles laterally compressed; leaves tremulous. POPULUS, p. 44.
ii. Leaf-petioles terete; leaves not tremulous.
j. Leaf-blades at least 3 times as long as they are broad.
k. Twigs brittle; fruit a very small capsule, falling in spring. SALIX, p. 34.
kk. Twigs tough; fruit a fleshy drupe, falling in late summer or autumn. PRUNUS, p. 152.
jj. Leaf-blades not more than twice as long as they are broad.
k. Leaf-blades about twice as long as they are broad.
l. Margin of leaves singly serrate; fruit fleshy.
m. Lenticels conspicuous; pith whitish or brownish; bark easily peeled off in papery layers; buds ovoid. PRUNUS, p. 152.
mm. Lenticels inconspicuous; pith greenish; bark not separable into papery layers; buds narrow-conical. AMELANCHIER, p. 149.
ll. Margin of leaves doubly serrate; fruit not fleshy.
m. Trunk fluted; fruit inclosed within a halberd-shaped involucre. CARPINUS, p. 83.
mm. Trunk not fluted; fruit not inclosed within a halberd-shaped involucre.
n. Bark of trunk gray-brown, broken into narrow, flattish pieces loose at the ends; fruit in hop-like strobiles. OSTRYA, p. 81.
nn. Bark of trunk white, yellow or dark brown, platy or cleaving off in papery layers; fruit not in hop-like strobiles. BETULA, p. 84.
kk. Leaf-blades almost as broad as they are long.
l. Lower side of leaves more or less downy; sap milky; leaves not crowded on short, spur-like branchlets; fruit berry-like, black. MORUS, p. 135.
ll. Lower side of leaves glabrous; sap not milky; leaves crowded on short, spur-like branchlets; fruit a large, green pome. PYRUS, p. 142.
ee. Margin of leaves distinctly lobed.
f. Fruit an acorn. QUERCUS, p.96.
ff. Fruit not an acorn.
g. Leaves fan-shaped, with many fine veins radiating from the base of the blade. GINKGO, p. 3.
gg. Leaves not fan-shaped, without many fine veins radiating from the base of the blade.
h. Leaf-lobes entire.
i. Leaf-petioles 5-6 inches long; leaves lustrous above; twigs not aromatic when bruised. LIRIODENDRON, p. 137.
ii. Leaf-petioles about 1 inch long; leaves dull above; twigs spicy-aromatic when bruised. SASSAFRAS, p. 139.
hh. Leaf-lobes sinuate-toothed to serrate.
i. Leaf-lobes coarsely sinuate-toothed. PLATANUS, p. 141.
ii. Leaf-lobes serrate.
j. Branches armed with stiff, sharp thorns; sap not milky. CRATAEGUS, p. 151.
jj. Branches unarmed; sap milky. MORUS, p. 135.
cc. Leaves opposite or whorled.
d. Margin of leaves entire or only slightly undulate.
e. Leaves 3-5 inches long; spray fine; fruit an ovoid, scarlet drupe. CORNUS, p. 202.
ee. Leaves 5-12 inches long; spray coarse; fruit a long, slender-cylindrical capsule. CATALPA, p. 222.
dd. Margin of leaves serrate to lobed.
e. Margin of leaves finely serrate. VIBURNUM, p. 229.
ee. Margin of leaves distinctly lobed. ACER, p. 172.
aa. Leaves compound.
b. Leaves alternate.
c. Leaves simple-pinnate.
d. Branchlets armed with short, sharp prickles. ROBINIA, p. 169.
dd. Branchlets unarmed.
e. Leaflets entire with the exception of 2 or more coarse, glandular teeth at the base. AILANTHUS, p. 171.
ee. Leaflets serrate the entire length.
f. Upper leaflets less than 1 inch broad.
g. Trunk and large branches armed with stout spines; leaflets 3/4-1-1/2 inches long. GLEDITSIA, p. 165.
gg. Trunk and large branches unarmed; leaflets 2-3 inches long. PYRUS, p. 142.
ff. Upper leaflets 1-5 inches broad.
g. Leaflets 5-11; pith homogeneous. CARYA, p. 66.
gg. Leaflets 11-23; pith chambered. JUGLANS, p. 60.
cc. Leaves bi-pinnate.
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.
Michigan Trees: A Handbook of the Native and Most Important Introduced Species

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