ARTIFICIAL KEYS, HOW MADE AND USED

An artificial key is a scheme for easily and quickly identifying any unknown object under consideration. This bulletin being devoted to the trees of Michigan, the keys to be found herein are intended to make it possible for any person, even if his botanical training be meager, to determine what trees grow about any home or farm, city park or woodlot in the state. With certain modifications and limitations they may prove useful in other localities as well. Since many people are unfamiliar with the construction and use of keys for identification, it will be the purpose of the following paragraphs to briefly outline the principles of construction and the manner of using the keys to be found here.

The keys are based on the most striking similarities and differences which the various parts of trees—twigs, buds, leaves, etc.—show, i. e., those characters which stand out in bold relief, which catch the eye at first sight. Two alternatives are presented, either a character is or is not present; these are the only choices possible. Indeed, further divisions are unnecessary and only lead to confusion and possible oversight. The two diametrically opposed characters are said to be coördinate in rank. In the keys they are preceded by the same letter or letters (a and aa or b and bb, etc.) and are set at the same distance from the left margin of the page. Often a and aa, or b and bb are further divisible into other groups; in every case the characters are opposed (a positive and a negative) and are given coördinate rank. It is desirable for mechanical reasons to divide the main divisions of the key more or less evenly, but this is not always feasible, nor should it be religiously adhered to.

Suppose as a concrete example that it is desired to construct a key to distinguish five houses in a city block. Three of these are of wood construction, two are of brick, and of the two wooden houses one is painted white and one brown. We may classify them as follows:

a.	Houses wood.
b.		Body paint brown.		Smith’s house
bb.		Body paint white.
		c.	Trimmings green color.	Jones’ house
cc.			Trimmings slate color.	Brown’s house
aa.	Houses brick.
	b.	Roof gray slate.		Johnson’s house
	bb.	Roof red tile.		Public Library

It is desirable in many cases to add other characters to lessen the liability of confusion, where the characters chosen are not distinct, and to show the user that he is on the right track. Thus, in the example just given, green color and slate color under certain defects of the eye, a coating of dust or deficiencies of the light might be confused, under which circumstances we would be justified in adding to the above statements without the criticism of description being made. Thus:

bb.
	c.	Trimmings green color; gable roof.	Jones’ house
	cc.	Trimmings slate color; mansard roof.	Brown’s house

The keys in this bulletin are constructed on the above principles. They are not in all cases as simple as the illustration just used, but if the reader has mastered the house illustration he will have little or no trouble with the larger keys. Suppose that (during a summer stroll) you come across a large tree with rough, hard bark and thin, lobed leaves which you do not know. Turning to the Summer Key to the Genera you find first a. Leaves simple, and contrasted with this aa. Leaves compound. Obviously the leaf is simple and the genus sought lies in that portion of the key preceding aa, i.e., under a. b and bb under a give you a choice between Leaves needle-shaped, awl-shaped, strap-shaped or scale-like and Leaves broad and flat. The leaf being broad and flat you pass to c and cc under bb. Here you have a choice between Leaves alternate or clustered and Leaves opposite or whorled. Inspection shows the arrangement to be opposite, and you know that the genus sought lies in that portion of the key between cc and aa. Passing to d and dd under cc gives the choice between Margin of leaves entire or only slightly undulate and Margin of leaves serrate to lobed. The leaf is deeply lobed. It is then either a Viburnum or an Acer, and the fact that the leaf-margin is lobed and not finely serrate brings the chase down to Acer. Before going further go back over the key and make careful note of the particular characters which were used to separate this genus from the other genera and try to fix these in mind. This done, turn to the page indicated, where you will find a Summer Key to the Species of Acer. You run through this key in the same manner that you did the genus key. If you have been careful in your search you will finally stop at Acer saccharum. Once more pause and go back over this key and try to fix in mind the characters which were used to separate the various species, especially the difference between your tree and Acer platanoides, which it so closely resembles. This done, turn to the page indicated and compare the characters of your tree with the drawings and descriptions. If you are satisfied with your diagnosis, well and good. If you find that you are wrong, go over the keys again and find wherein you were led astray.

Before you leave the tree take a sample of leaf properly labeled which you can press between the pages of an old magazine and save for future reference. Do this with other trees which you may find and when you get home lay them out side by side so that the labels will not show and compare them. A few trials of this kind will serve to form a mental picture of each leaf which you will remember.

A very helpful practice for the beginner is that of making keys based upon various characters. Practice keys of this kind will bring out the differences and likenesses of trees as will no other means, and characters which have hitherto escaped the eye will be prominently brought forward. Nor should the student take his characters from books, but rather should he go to the woods and get his knowledge first hand.

It is hardly necessary to state that the key is a valuable crutch while learning to walk, but once the leg is strong enough to bear the weight it should be discarded, lest it become a burden. A key has for its main object the guidance of the student through the preliminary steps leading to a more intimate knowledge of the trees. When once he knows a tree, instinctively, because of long acquaintance with it, just as he knows people, then the need for a key will have ceased.

SUMMER KEY TO THE GENERA [A]

Leaves simple.

Leaves needle-shaped, awl-shaped, strap-shaped or scale-like.

Leaves in clusters of 2-many.

Leaves in clusters of 2-5, sheathed, persistent forseveral 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.

Leaves opposite.

Twigs flattened; leaves all of one kind, scale-like,decurrent on the stem; fruit a small, pale browncone.

THUJA, p. [31].

ee.

Twigs essentially terete; leaves of two kinds, eitherscale-like, or else awl-shaped, often both kinds onthe same branch, not decurrent on the stem; fruitberry-like, bluish.

JUNIPERUS, p. [33].

dd.

Leaves alternate or spirally-whorled.

Leaves flattened, soft to the touch.

Leaves 1/2-1-1/4 inches long, sessile, aromatic; cones2-4 inches long; bark of trunk with raised blisterscontaining resin.

ABIES, p. [27].

ff.

Leaves seldom over 1/2 inch long, short-petioled,not aromatic; cones about 3/4 inch long; bark oftrunk without raised blisters.

TSUGA, p. [29].

ee.

Leaves 4-sided, harsh to the touch.

PICEA, p. [18].

bb.

Leaves broad and flat.

Leaves alternate or clustered, never opposite nor whorled.

Margin of leaves entire or only slightly undulate.

Leaves heart-shaped or rounded; fruit a legume.

CERCIS, p. [167].

ee.

Leaves oval, ovate or obovate; fruit not a legume.

Branches armed with stout, straight spines; fruitlarge, orange-like.

MACLURA, p. [133].

ff.

Branches without spines; fruit small, not orange-like.

Fruit an acorn.

QUERCUS, p. [96].

gg.

Fruit a drupe or berry.

Twigs spicy-aromatic when bruised; leaves ofmany shapes on the same branch.

SASSAFRAS, p. [139].

hh.

Twigs not spicy-aromatic; leaves not of manyshapes on the same branch.

Leaves thick, abruptly pointed, very lustrousabove, not clustered at the ends of thebranches.

NYSSA, p. [209].

ii.

Leaves thin, long-pointed, not lustrousabove, clustered at the ends of the branches.

CORNUS, p. [202].

dd.

Margin of leaves serrate, toothed or lobed.

Margin of leaves serrate to toothed.

Branches armed with stiff, sharp thorns.

CRATAEGUS, p. [151].

ff.

Branches not armed.

Base of leaves decidedly oblique.

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 arebroad, oval to ovate.

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.

Teeth coarse, 2-5 per inch of margin.

Leaves very glabrous both sides; fruit aprickly bur.

Leaves 3-5 inches long, very lustrousbeneath; 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, atleast beneath; fruit not a prickly bur.

Leaves 2-4 inches long, broadly ovate tosuborbicular; fruit a very small capsule,falling in spring.

POPULUS, p. [44].

jj.

Leaves 4-7 inches long, oblong-lanceolateto obovate; fruit an acorn, falling inautumn.

QUERCUS, p. [96].

hh.

Teeth fine, 6-many per inch of margin.

Leaf-petioles laterally compressed; leavestremulous.

POPULUS, p. [44].

ii.

Leaf-petioles terete; leaves not tremulous.

Leaf-blades at least 3 times as long asthey are broad.

Twigs brittle; fruit a very small capsule,falling in spring.

SALIX, p. [34].

kk.

Twigs tough; fruit a fleshy drupe, fallingin late summer or autumn.

PRUNUS, p. [152].

jj.

Leaf-blades not more than twice as longas they are broad.

Leaf-blades about twice as long as theyare broad.

Margin of leaves singly serrate; fruitfleshy.

Lenticels conspicuous; pith whitishor brownish; bark easily peeledoff in papery layers; buds ovoid.

PRUNUS, p. [152].

mm.

Lenticels inconspicuous; pithgreenish; bark not separable intopapery layers; buds narrow-conical.

AMELANCHIER, p. [149].

ll.

Margin of leaves doubly serrate; fruitnot fleshy.

Trunk fluted; fruit inclosed withina halberd-shaped involucre.

CARPINUS, p. [83].

mm.

Trunk not fluted; fruit not inclosedwithin a halberd-shapedinvolucre.

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 ordark brown, platy or cleaving offin papery layers; fruit not inhop-like strobiles.

BETULA, p. [84].

kk.

Leaf-blades almost as broad as theyare long.

Lower side of leaves more or lessdowny; sap milky; leaves not crowdedon short, spur-like branchlets; fruitberry-like, black.

MORUS, p. [135].

ll.

Lower side of leaves glabrous; sapnot milky; leaves crowded on short,spur-like branchlets; fruit a large,green pome.

PYRUS, p. [142].

ee.

Margin of leaves distinctly lobed.

Fruit an acorn.

QUERCUS, p.96.

ff.

Fruit not an acorn.

Leaves fan-shaped, with many fine veins radiatingfrom the base of the blade.

GINKGO, p. [3].

gg.

Leaves not fan-shaped, without many fine veinsradiating from the base of the blade.

Leaf-lobes entire.

Leaf-petioles 5-6 inches long; leaves lustrousabove; twigs not aromatic when bruised.

LIRIODENDRON, p. [137].

ii.

Leaf-petioles about 1 inch long; leaves dullabove; twigs spicy-aromatic when bruised.

SASSAFRAS, p. [139].

hh.

Leaf-lobes sinuate-toothed to serrate.

Leaf-lobes coarsely sinuate-toothed.

PLATANUS, p. [141].

ii.

Leaf-lobes serrate.

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.

Margin of leaves entire or only slightly undulate.

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.

Margin of leaves finely serrate.

VIBURNUM, p. [229].

ee.

Margin of leaves distinctly lobed.

ACER, p. [172].

aa.

Leaves compound.

Leaves alternate.

Leaves simple-pinnate.

Branchlets armed with short, sharp prickles.

ROBINIA, p. [169].

dd.

Branchlets unarmed.

Leaflets entire with the exception of 2 or morecoarse, glandular teeth at the base.

AILANTHUS, p. [171].

ee.

Leaflets serrate the entire length.

Upper leaflets less than 1 inch broad.

Trunk and large branches armed with stoutspines; leaflets 3/4-1-1/2 inches long.

GLEDITSIA, p. [165].

gg.

Trunk and large branches unarmed; leaflets 2-3inches long.

PYRUS, p. [142].

ff.

Upper leaflets 1-5 inches broad.

Leaflets 5-11; pith homogeneous.

CARYA, p. [66].

gg.

Leaflets 11-23; pith chambered.

JUGLANS, p. [60].

cc.

Leaves bi-pinnate.

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 - 2-1/2inches long.

GYMNOCLADUS, p. [163].

bb.

Leaves opposite.

Leaves pinnately compound; fruit a samara.

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].

WINTER KEY TO THE GENERA [B]

Leaves persistent and green throughout the winter, needle-shaped,awl-shaped or scale-like.

Leaves in clusters of 2-5, sheathed.

PINUS, p. [5].

bb.

Leaves solitary, not clustered.

Leaves opposite.

Twigs flattened; leaves all of one kind, scale-like,decurrent on the stem; fruit a small, pale brown cone.

THUJA, p. [31].

dd.

Twigs essentially terete; leaves of two kinds, eitherscale-like, or else awl-shaped, often both kinds on thesame branch, not decurrent on the stem; fruit berry-like,bluish.

JUNIPERUS, p. [33].

cc.

Leaves alternate or spirally-whorled.

Leaves flattened, soft to the touch.

Leaves 1/2 - 1-1/4 inches long, sessile, aromatic; cones2-4 inches long; bark of trunk with raised blisterscontaining resin.

ABIES, p. [27].

ee.

Leaves seldom over 1/2 inch long, short-petioled, notaromatic; cones about 3/4 inch long; bark of trunkwithout raised blisters.

TSUGA, p. [29].

dd.

Leaves 4-sided, harsh to the touch.

PICEA, p. [19].

aa.

Leaves not persistent and green throughout the winter, butdeciduous in early autumn.

Twigs, branches or trunks armed with stiff, sharp prickles,spines or thorns.

Thorns or spines not exceeding 1/2 inch in length on thebranches.

Spines in pairs at each node; buds rusty-hairy, 3-4superposed; fruit a flat pod.

ROBINIA, p. [169].

dd.

Spines one at each node; buds glabrous, not superposed;fruit orange-like.

MACLURA, p. [133].

cc.

Thorns or spines much exceeding 1/2 inch in length onthe branches.

Thorns usually branched, situated above the nodes;lateral buds superposed, the lower covered by bark;fruit a flat pod.

GLEDITSIA, p. [165].

dd.

Thorns unbranched on twigs, situated at the nodes;lateral buds not superposed, not covered by bark;fruit a small pome.

CRATAEGUS, p. [151].

bb.

Twigs, branches or trunks unarmed.

Leaf-scars mainly crowded on short, stout, lateral shoots.

Bundle-scar 1; fruit a cone, usually present.

LARIX, p. [17].

dd.

Bundle-scars 2; fruit a globose drupe falling inautumn.

GINKGO, p. [3].

cc.

Leaf-scars distributed along the lateral branches.

Leaf-scars (or some of them) 3 at a node, i. e.,whorled.

CATALPA, p. [223].

dd.

Leaf-scars 1-2 at a node, i.e., not whorled.

Leaf-scars 2 at a node, i.e., opposite.

Terminal buds 1/2 - 1-1/2 inches long, resin-coated;twigs very stout.

AESCULUS, p. [195].

ff.

Terminal buds rarely exceeding 1/2 inch in length,not resin-coated; twigs not conspicuously stout.

Leaf buds with 1 pair of scales visible.

Buds scurfy-pubescent.

VIBURNUM, p. [229].

hh.

Buds glabrous.

CORNUS, p. [203].

gg.

Leaf buds with 2 or more pairs of scales visible.

Bundle-scars usually 3, distinct, separated.

ACER, p. [174].

hh.

Bundle-scars many, minute, more or less confluentin a U-shaped line.

FRAXINUS, p. [211].

ee.

Leaf-scars 1 at a node, i.e., alternate.

Bundle-scars 1-3.

Bundle-scar only 1, or appearing as 1.

Twigs bright green, spicy-aromatic; bundle-scarappearing as a horizontal line; terminalbud present; pith homogeneous.

SASSAFRAS, p. [139].

hh.

Twigs brownish, not spicy-aromatic; bundle-scarappearing as a large dot; terminal budabsent; pith chambered.

CELTIS, p. [131].

gg.

Bundle-scars 3 or in 3 compound, but distinctgroups.

Terminal bud present.

Stipule-scars present.

First scale of lateral bud directly in front,i.e., exactly above the center of the leaf-scar;twigs brittle; pith somewhat star-shapedin cross-section.

POPULUS, p. [45].

jj.

First scale of lateral bud not directly infront, i. e., to one side of the center of theleaf-scar; twigs not brittle; pith circularin cross-section.

PRUNUS, p. [153].

ii.

Stipule-scars absent.

Buds bright to dark red, the terminal1/8 - 1/4 inch long.

Branches contorted, bearing manyshort, spur-like branchlets; fruit anapple an inch or more in diameter, lightgreen.

PYRUS, p. [143].

kk.

Branches not contorted, not bearingshort, spur-like branchlets; fruit berry-like,1/2 inch long, blue-black.

NYSSA, p. [209].

jj.

Buds brownish to gray, the terminal exceeding1/4 inch in length.

Buds narrow-conical, sharp-pointed;leaf-scars small, narrowly crescent-shaped;twigs about 1/16 inch thick;pith homogeneous; fruit berry-like, notpresent.

AMELANCHIER, p. [149].

kk.

Buds broadly conical to ovoid, blunt-pointed;leaf-scars conspicuous, broadlyheart-shaped; twigs about 1/4 inchthick; pith chambered; fruit a nut,often present.

JUGLANS, p. [61].

hh.

Terminal bud absent (sometimes present onshort shoots of Betula).

Stipule-scars present.

Bud-scale only 1 visible; twigs brittle.

SALIX, p. [34].

jj.

Bud-scales 2 or more; twigs not brittle.

Bark smooth, close, warty or peelinginto papery layers, but not flaky norrough-ridged.

Tip of bud appressed; fruit berry-like.

CELTIS, p. [131].

ll.

Tip of bud not appressed; fruit notberry-like.

Trunk fluted; catkins not presentin winter; lenticels not elongatedhorizontally; low tree or bushyshrub.

CARPINUS, p. [83].

mm.

Trunk not fluted; catkins usuallypresent in winter; lenticels elongatedhorizontally; large trees.

BETULA, p. [85].

kk.

Bark flaky or rough-ridged, not wartynor peeling off in papery layers.

Bundle-scars depressed, conspicuous;bark thick, more or less deeply furrowed.

ULMUS, p. [123].

ll.

Bundle-scars not depressed, inconspicuous;bark thin, broken into narrow,flattish strips, loose at the ends.

OSTRYA, p. [81].

ii.

Stipule-scars absent.

Buds silky-pubescent, depressed; twigsstout, clumsy, blunt, with conspicuousleaf-scars.

GYMNOCLADUS, p. [163].

jj.

Buds glabrous, not depressed; twigs slender,with inconspicuous leaf-scars.

Buds 1/8 inch long, obtuse, somewhatflattened and appressed; pith with reddishlongitudinal streaks.

CERCIS, p. [167].

kk.

Buds 1/8-1/4 inch long, acute, not flattenednor appressed; pith without reddishstreaks.

PRUNUS, p. [153].

ff.

Bundle-scars 4-many.

Bundle-scars in a single U-shaped line.

Terminal bud present; fruit berry-like; ashrub or small tree.

PYRUS, p. [143].

hh.

Terminal bud absent; fruit not berry-like;large trees.

Stipule-scars present; twigs slender.

Stipule-scars encircling the twig; leaf-scarsnearly surrounding the bud; barkpeeling off in thin plates, exposing thelighter colored inner bark.

PLATANUS, p. [141].

jj.

Stipule-scars not encircling the twig; leaf-scarsnot nearly surrounding the bud;bark thick, rough-ridged, not exposing theinner bark.

ULMUS, p. [123].

ii.

Stipule-scars absent; twigs very stout.

Bundle-scars usually not more than 5.

GYMNOCLADUS, p. [163].

jj.

Bundle-scars usually 6-12.

AILANTHUS, p. [171].

gg.

Bundle-scars variously grouped or scattered,but not in a single line.

Terminal bud present.

Stipule-scars present.

Stipule-scars encircling the twig; visiblebud-scales 2, united.

LIRIODENDRON, p. [137].

jj.

Stipule-scars not encircling the twig; visiblebud-scales more than 2, not united.

Buds 4 times as long as broad, notclustered at the tips of vigorous shoots;fruit a prickly bur.

FAGUS, p. [93].

kk.

Buds not 4 times as long as broad,usually clustered at the tips of vigorousshoots; fruit an acorn.

QUERCUS, p. [98].

ii.

Stipule-scars absent.

CARYA, p. [67].

Terminal bud absent (occasionally present inCastanea).

Bud at end of twig very obliquely unsymmetrical,mucilaginous when chewed.

TILIA, p. [201].

ii.

Bud at end of twig symmetrical, not mucilaginouswhen chewed.

Bud-scales 2-3 visible; pith star-shaped incross-section; sap not milky; fruit aprickly bur, present; large tree.

CASTANEA, p. [95].

jj.

Bud-scales 4-8 visible; pith not star-shapedin cross-section; sap milky; fruitberry-like, not present; small tree.

MORUS, p. [135].