bio

Taxonomy: Classifying and Naming Organisms

After completing this exercise, you will be able to

1. define common name, scientific name, binomial, genus, specific epithet, species, taxonomy, phylogenetic system, dichotomous key, herbarium;

2. distinguish common names from scientific names;

3. explain why scientific names are preferred over common names in biology;

4. identify the genus and specific epithet in a scientific binomial;

5. write out scientific binomials in the form appropriate to the Linnean system;

6. construct a dichotomous key;

7. explain the usefulness of an herbarium;

8. use a dichotomous key to identify plants, animals, or other organisms as provided by your instructor.

Introduction We are all great classifiers. Every day, we consciously or unconsciously classify and categorize the objects around us. We recognize an organism as a cat or a dog, a pine tree or an oak tree. But there are numerous kinds of oaks, so we refine our classification, ivin the trees distinguishing names such as "red oak," "white oak," or "bur oak." These are examples o common name names with which you are probably iiillsHamiliar. - ---scientists are continuall exchanging information about living organisms. But not all scientists speak the same language. Th ommon nam "white oak," familiar to an An:erican, is probably not familiar to a Spanish ~logist, even though the tree we know as white oak may exist in Spain as well as in our own backyard. Moreover, even within our own language, the same organism can have several common names. For example, within North America a gopher is also called a ground squirrel, a pocket mole, and a groundhog. On the other hand, the same common name may describe many different organisms; there are more than 300 different trees called "mahogany"! To circumvent the problems associated with common names, biologists use t[ctenti1i9

0 a§9 !hat are ni ue to each kin · and tha ar u throu hout A cientific nam js two-parted, a bin mial. The.iirst word of the binomial designates the group to which

the organism be ongs; this is the enus arne (the plural of genus is genera). All oak trees belon to the genus Quercus, a word derived from Latin . . ach kind of organism within a genus is given a ecific e ithe Thus, the scientific name for white oak is Quercus alba (~Clfic ep1tljl is_Ellzg), while that of bur oa IS Quercus macrocarpa ~is macrocarl!£!1

Notice that the genus name is always capitalized; the specific e.Pithet usually is not capitalized (although it can be if it is the proper name oi' a person or place). The binomial is written in italics (since theseare Latin names); if italics are not available, the genus name and specific epithet are underlined.

You will hear discussion of "species" of organisms. For example, on a field trip, you may be asked "What ~ecies is this tree?" Assuming you are looking at a white oak, your reply would be "Quercus alba." .The scientific name of the species includes both the enus and s ecifi · - If a species is name more an once within a document, it is accepted convention to write out the full genus

name and specific epithet the first time and to abbreviate the genus name every time thereafter. For example, if white oak is being described, the first use is written Quercus alba, and each subsequent naming appears as Q. alba.

Similarly, when a number of species, all of the same genus, are being listed, the accepted convention is to write both the genus name and specific epithet for the first species and to abbreviate the genus name for each species listed thereafter. Thus, it is acceptable to list the scientific names for white oak and bur oak as Quercus alba and . macrocarpa, respectively.

axonom ·s the science of classification (categorizing) and nomenclature (naming). Biologists prefer a system that in 1cates the evolutionary relationships among organisms. To this end, classification became a j;i~ylogenetiD

(SYs,§ that is, one indicating the cmrent understanding of evolutionary ancestry among organism~

225

f

Current taxonomic thought separates all living organisms into six kingdoms:

1. Kingdom Bacteria (prokaryotic cells of great diversity, and that include pathogens) 2. Kingdom Archaea (prokaryotic organisms that are evolutionarily between eukaryotes and bacteria) 3. Kingdom Protista (as collection of lineages, some single-celled and some multi-celled; includes euglenoids,

ciliates, dinoflagellates, amoebas, and many groups of "algae") 4. Kingdom Fungi (fungi) 5. Kingdom Plantae (plants) 6. Kingdom Animalia (animals)

Let's consider the s~ientific system of classification, using ourselves as examples. All members of our species belong to Kingdom Animalia (arumals):

• Phylum Chordata (animals with a notochord) • Class Mammalia (animals with mammary glands and skin with hair) • Order Primates (mammals that walk upright on two legs) • Family Hominidae (human forms existin and extinct • enus omo mankind) • Specific epithet sapiens (wise) • Species: Homo sapiens

The more closely related evolutionarily two organisms are, the more categories they share. You and I are different individuals of the same species. We share the same genus and specific epithet, Homo and sapiens. A creature believed to be a close, extinct ancestor walked the Earth 1.5 million years ago. That creature shared our genus name but had a different specific epithet, erectus. Thus, Homo sapiens and H. erectus are different species.

Like all science, taxonomy is subject to change as new information becomes available. Modifications are made to reflect revised interpretations.

To classify organisms, you must first identify them. A taxonomic key helps to identify an object or organism unknown to you but that someone else has described . The user chooses between alternative characteristics of the unknown object and, by making the correct choices, arrives at the name of the object.

Keys that are based on successive choices between two alternatives are known as dichotomous keys (dichotomous means "to fork into two equal parts"). When using a key, always read both choices even though the first appears to describe the subject. Don' t guess at measurements; use a ruler. Since living organisms vary in their characteristics, don't base your conclusion on a single specimen if more are available.

MATERIALS

Per lab room: • several meter sticks or metric height charts taped to a wall

PROCEDURE

1. Suppose the geometric shapes below have unfamiliar names. Look at the d ichotomous key following the figures. Notice there is a la and a lb . Start with la. If the description in la fits the figure you are observing better than description lb, then proceed to the choices listed under 2, as shown at the end of line l a. If la does not describe the figure in question, lb does . Looking at the end of line lb, you see tha t the figure would be called an Elcric.

2. Use the key provided to determine the hypothetical name for each object. Write the n ame benea th the object and then check with your instructor to see if you have made the correct choices.

226 E X E R C I S E 1 8

Key

1a. Figure with distinct corners 2

1b. Figure without distinct corners Elcric

2a. Figure with 3 sides 3

2b. Figure with 4 or more sides 4

3a. All sides of equal length Legnairt

3b. Only 2 sides equal Legnairtosi

4a. Figure with only right angles Eraqus

4b. Figure with other than right angles Nogatco

3. Now you will construct a dichotomous key, using your classmates as subjects. The class should divide up into groups of eight (or as evenly as the class size will allow). Working with the individuals in your group, fill in Table 18-1, measuring height with a metric ruler or the scale attached to the wall.

4. To see how you might plan a dichotomous key, examine the following branch diagram below. If there are both men and women in a group, the most obvious first split is male/female (although other possibilities for the split could be chosen as well). Follow the course of splits for two of the men in the group.

Note that each choice has only two alternatives. Thus, we split into "under 1.75 m" and "1.75 m or taller." Likewise, our next split is into "blue eyes" and "nonblue eyes" rather than all the possibilities.

under 1.75m

blonde hair (Jim Perry)

male

blue eyes

1.75 m or taller

brown hair (Dave Morton)

start

non blue eyes

female

5. On a separate sheet of paper, construct a branch diagram for your group using the characteristics in Table 18-1 and then condense it into the dichotomous key that follows. When you have finished, exchange your key with that of an individual in another group. Key out the individuals in the other group without speaking until you believe you know the name of the individual you are examining. Ask that individual if you are correct. If not, go back to find out where you made a mistake, or possibly where the key was misleading. (Depending on how you construct your key, you may need more or fewer lines than have been provided.)

Taxonomy: Classifying and Naming Organisms 227

TABLE 18·1 Characteristics of Students

Student (name) Sex (m/f) Height (m) Eye Color Hair Color Shoe Size

1.

2 .

3.

4.

5.

6.

7.

8.

Key to Students in Group---------------

1a.

1b.

2a .

2b.

3a.

3b.

4a .

4b.

5a.

5b.

6a.

6b.

?a.

?b.

8a.

8b.

A. Some Microscopic Members of the Freshwater Environment (About 30 min.)

Supp ose you want to identify the specimens in some pond water. The easiest way is to key them ou t with a dich otom ous key, n ow tha t you know how to use one. In this section, you will do just that.

•, 228 E X E R C I S E 1 8

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MATERIALS

Per student: Per student group (table): • compound microscope • cultures of freshwater organisms • microscope slide • one disposable p las tic p ipet per culture • coverslips • methylcellulose in dropping b ottle • d issecting n eedle

PROCEDURE

1. Obtain a clean glass microscop e slid e and clean coverslip . 2. Using a d isposable plastic p ip et or dissecting n eedle, withdraw a small amount of the culture provided. 3. Place one d rop of the culture on the center of the slide. 4. Gently lower the coverslip onto the liquid . 5. Using your compound light m icroscop e, observe your wet mount. Focu s firs t w ith the low-power objective

and then with the m edium or high-dry objective, d ep ending on the size of the organism in the field of view. 6. Concentrate you r observa tion on a sin gle specimen , keying out the sp ecimen u sing the Key to Selected

Freshwater Inhabitants that follows. 7. In the space p rovided , write the scientific name of each organism you identify. After each identification,

have your instructor verify your conclusion . 8. Clean and reu se you r slide after each id entification .

Key to Selected Freshwater Inhabitants

1 a. Filamentous organism consisting of green, chloroplast-bearing threads 2

1 b. Organism consisting of a single cell or nonfilamentous colony 4

2a. Filament branched , each cell mostly filled with green chloroplast Cladophora

2b. Filament unbranched 3

3a. Each cell of filament containing 1 or 2 spiral-shaped green chloroplasts Spirogyra

3b. Each cell of filament containing 2 star-shaped green chloroplasts Zygnema

4a. Organism consisting of a single cell 5

4b. Organism composed of many cells aggregated into a colony 6

5a. Motile, teardrop-shaped or spherical organism Chlamydomonas

5b. Nonmotile, elongate cell on either end ; clear, granule-containing regions at ends Closterium

6a. Colony a hollow round ball of more than 500 cells; new colonies may be present inside larger colony Volvox

6b. Colony consisting of less than 50 cells 7

?a. Organism composed of a number of tooth-shaped cells Pediastrum

7b. Colony a loose square or rectangle of 4-32 spherical cells Gonium

Organism l is ______________________________________________________________________ ___

Organism2 is ______________________________________________________________________ ___

Organism 3is ______________________________________________________________________ ___

Organism 4is ______________________________________________________________________ ___

Organism S is __________________________________________________________________________ __

Organism 6is------------------------------------------------------------------~----- Organism 7is ______________________________________________________________________ ___

Organism S is ______________________________________________________________________ ___

Taxonomy: Classifying and Naming Organisms 229

B. Common Trees and Shrubs (About 1 hour)

Suppose you want to identify the trees growing on your campus or in your yard at home. Without having an expert present, you can now do that, because you know how to use a taxonomic key. But how can you be certain that you have keyed your specimen correctly?

Typically, scientists compare their tentative identifications against reference specimens-that is, preserved organisms that have been identified by an expert taxonomist (a person who names and classifies organisms). If you are identifying fishes or birds, the reference specimen might be a bottled or mounted specimen with the name on it. In the case of plants, reference specimens most frequently take the form of herbarium mounts (Figure 18-1) of the plants. An herbarium (plural, herbaria) is a repository, a museum of sorts, of preserved plants. The taxonomist flattens freshly collected specimens in a plant press. They are then dried and mounted on sheets of paper.

Herbarium labels are affixed to the sheets, indicating the scientific name of the plant, the person who collected it, the location and date of collection, and often pertinent information about the habitat in which the plant was found.

It is likely that your school has an herbarium. If so, your instructor may show you the collection. To some, this endeavor may seem boring, but herbaria serve a critical function. The appearance or disappearance of plants from the landscape often gives a very good indication of environmental change. An herbarium records the diversity of plants in the area, at any point in history since the start of the collection. ~

MATERIALS

Per student group (table): • set of eight tree twigs with leaves (fresh or herbarium Figure 18-1 A typical herbarium mount.

specimens) or • trees and shrubs in leafy condition (for an outdoor lab)

PROCEDURE Use the appropriate following key to identify the tree and shrub specimens that have been provided in the lab or that you find on your campus. Refer to the Glossary to Tree Key (page 236) and Figures 18-2 through 18-9 (pages 230-232) when you encounter an unfamiliar term. When you have finished keying a specimen, confirm your identification by checking the herbarium mounts or asking your instructor.

Note: Some descriptions within the key have more characteristics than your specimen will exhibit. For example, the key may describe a fruit type when the specimen doesn't have a fruit on it. However, other specimen characteristics are described, and these should allow you to identify the specimen in most cases.

Note: The keys provided are for selected trees of your area. In nature, you will find many more genera than can be identified by these keys.

230 E X E R C I S E 1 8

Figure 18-2 Structure of a typical plant {bean).

Common names within parentheses follow the scientific name. A metric ruler is provided below for use where measurements are required.

axillary bud

toothed margin

node

leaflet (lateral)

(a) toothed

axillary bud

(b) lobed

Figure 18-3 Simple leaves. Figure 18-4 Pinnately compound leaf.

margin entire

spine (thorn) base (obtuse)

node :::::::::;;;iif!~:_

internode

Figure 18-5 Simple leaves-alternating. Figure 18-6 Simple leaves-opposite.

(a) pith chambered (b) pith solid

Figure 18-7 Palmately compound leaf. Figure 18-8 Pith types.

Taxonomy: Classifying and Naming Organisms 231

I

(a) pome (apple, hawthorne)

(e) capsule (buckeye)

Figure 18-9 Fruit types.

wing

{b) schizocarps (maple)

(f) pods (pea)

(c) samaras (ash) {d) nuts (oak )

(g) drupe (cherry)

1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

ce ntimeters

Key to Some Common Genera of Trees of the Midwestern and Eastern United States and Canada

1a.

1b.

2a .

2b.

3a.

3b.

4a.

Leaves broad and flat; plants producing flowers and fruits (angiosperms)

Leaves needlelike or scalelike ; plants producing cones, but no flowers or fruits

(gymnosperms)

Leaves compound

Leaves simple

Leaves alternate

Leaves opposite

Leaflets short and stubby, less than twice as long as broad; branches armed

with spines or thorns ; fruit a beanlike pod

4b. Leaflets long and narrow, more than twice as long as broad ; trunk and branches

Sa .

unarmed ; fruit a nut

Leaflet margin without teeth; terminal leaflet present; small deciduous spines at

leaf base

Sb. Leaflet margin with fine teeth ; terminal leaflet absent; large permanent thorns on

trunk and branches

232 EX E R C I S E 1 8

2

22

3

9

4

7

5

6

Robinia (black locust)

Gleditsia (honey locust)

6a.

6b.

7a.

?b.

8a.

8b.

9a.

9b.

10a.

10b.

11a.

11 b.

12a.

12b.

13a.

13b.

14a.

14b.

15a.

15b.

16a.

16b.

17a.

17b.

18a.

18b.

19a.

19b.

20a.

20b.

21a.

21b.

Leaflets usually numbering less than 11; pith of twigs solid

Leaflets numbering 1 or more; pith of twigs divided into chambers

Leaflets pinnately arranged; fruit a light-winged samara

Leaflets palmately arranged ; fruit a heavy leathery spherical capsule

Leaflets mostly 3-5; fruit a schizocarp with curved wings

Leaflets mostly more than 5; samaras borne singly, with straight wings

Leaves alternate

Leaves opposite

Leaves very narrow, at least 3 times as long as broad; axillary buds flattened against stem

Leaves broader, less than 3 times as long as broad

Leaf margin without small, regular teeth

Leaf margin with small, regular teeth

Fruit a pod with downy seeds; leaf blade obtuse at base ; petioles flattened,

or if rounded, bark smooth

Fruit an acorn; leaf blade acute at base; petioles rounded ; bark rough

Leaves (at least some of them) whh lobes or other indentations in addition to

small , regular teeth

Leaves without lobes or other indentations except for small, regular teeth

Lobes asymmetrical , leaves often mitten-shaped

Lobes or other indentations fairly symmetrical

Branches thorny (armed) ; fruit a small applelike pome

Branches unarmed

Bark smooth and waxy, often separating into thin layers ; leaf base symmetrical

Bark rough and furrowed; leaf base asymmetrical

Leaf base asymmetrical , strongly heart-shaped , at least on one side

Leaf base acute, truncate, or slightly cordate

Leaf base asymmetrical ; bark on older stems (trunk) often warty

Leaf base symmetrical

Leaf blade usually about twice as long as broad, generally acute at base;

fruit fleshy

Leaf not much longer than broad, generally truncate at base; fruit a dry pod

Leaf tapering to a pointed tip, glandular at base

Leaf spoon-shaped with a rounded tip, no glands at base

Leaf margins with lobes and points ; fruit a schizocarp

Leaf margins without lobes or points; fruit a long capsule

Carya (hickory)

Juglans (walnut, butternut)

8

Aesculus (buckeye)

Acer (box elder)

Fraxinus (ash)

10

21

Salix (willow)

11

12

13

Populus (poplar, popple,

aspen)

Quercus (oaks)

14

16

Morus (mulberry)

15

Crataegus (hawthorne)

17

Betula (birch)

Ulmus (elm)

Tilia (basswood or linden)

18

Celtis (hackberry)

19

20

Populus (poplar, popple,

aspen)

Prunus (cherry)

Crataegus (hawthorne)

Acer (maple)

Catalpa (catalpa)

Taxonomy: Classifying and Naming Organisms 233

22a.

22b.

23a.

23b.

24a.

24b.

25a.

25b.

26a.

Leaves needlelike, with 2 or more needles in a cluster

Leaves needlelike or scalelike, occurring singly

Leaves more than 5 in a cluster, soft, deciduous, borne at the ends of conspicuous

stubby branches

Leaves 2-5 in a cluster

Leaves soft, not sharp to the touch

Leaves stiff or sharp and often unpleasant to touch

Leaves about 0.2 em and scalelike, overlapping

Leaves needlelike, appear to form two ranks on twig

Leaves with distinct petioles, 0.8-1.5 em long; twigs rough; female cones drooping

from branches

26b. Leaves without distinct petioles, 1-3 em long; twigs smooth; female cones erect on

branches

27a.

27b.

28a.

28b.

Leaves appear triangular-shaped, about 0.5 em, and tightly pressed to twig; cone

blue, berrylike

Leaves elongated and needlelike

Tree; leaves 4-sided, protrude stiffly from twig; female cones droop from branch

Shrub; leaves flattened, pressed close to twig at base; seed partially covered by a fleshy coat, usually red

Key to Some Common Genera of Trees of the Pacific Region of the United States and Canada

1a.

1b.

2a.

2b.

3a.

3b.

4a.

4b.

Sa.

5b.

6a.

Leaves broad and flat; plants producing flowers and fruits (angiosperms)

Leaves needlelike or scalelike; plants producing cones, but

no flowers or fruits (gymnosperms)

Leaves compound

Leaves simple

Leaves pinnately arranged

Leaves palmately arranged

Leaflets numbering 7; fruit a samara

Leaflets 15-17; fruit a nut

Leaflets numbering 3, lobed; fruit a schizocarp

Leaflets numbering more than 3; fruit a smooth or spiny capsule

Three or more equal-sized veins branching from leaf base

6b. Leaf with single large central vein with other main veins branching from the central vein

?a. Leaves opposite; fruit a schizocarp

?b. Leaves alternate

234 E X E R C I S E 1 8

23

24

Larix (larch, tamarack)

Pinus (pines)

25

27

Thuja (white cedar, arbor

vitae)

26

Tsuga (hemlock)

Abies (firs)

Uuniper, Eastern red cedar)

28

Picea (spruces)

Taxus (yew)

2

15

3

6

4

5

Fraxinus (ash)

Juglans (walnut)

Acer (box elder)

Aesculus (buckeye)

7

9

Acer (maple)

8

Sa.

Bb.

9a.

9b.

10a.

10b.

11a.

11 b.

12a.

12b.

13a.

13b.

14a.

14b.

15a.

15b.

16a.

16b.

17a.

17b.

18a.

18b.

19a.

19b.

20a.

20b.

21a.

21b.

22a.

Leaves nearly round in outline; fruit a pod

Leaves deeply lobed, very hairy beneath; fruit consisting of an aggregation of

many 1-seeded nutlets surrounded by long hairs

Leaf lobed ; fruit a nut

Leaf not lobed

Leaves opposite; fruit a drupe; halves of leaf remain attached by "threads" after

blade has been creased and broken

Leaves alternate

Upon crushing, blade gives off strong, penetrating odor

Blade not strongly odiferous upon crushing

Branch bark smooth, conspicuously red-brown; fruit a red or orange berry

Branch rough, not colored red-brown

Undersurface of leaves golden-yellow; fruit a spiny, husked nut

Leaves green beneath

Petiole hairy; leathery blade with a stubby spine at end of each main vein; fruit a nut

Petiole and leaf lacking numerous hairs, leaves long and narrow, more than twice as

long as wide

Leaves needlelike

Leaves scalelike

Leaves needlelike, with 2 or more needles in a cluster

Leaves needlelike , occurring singly

Needles 2-5 in a cluster

Needles 6 or more per cluster, soft, deciduous, borne at

the ends of stubby, conspicuous branches

Round scars on twigs where old needles have fallen off ; twigs smooth; needles soft

to the grasp; cones pointing upward with reference to stem

Twigs rough, with old needle petioles remaining

Needles angled, stiff, sharp, pointed, unpleasant to grasp; cones hanging

Needles soft, not sharp when grasped

Needles round in cross section, can be rolled easily between thumb and index finger;

needles less than 1.3 em long; cones small, less than 1.5 em

Needles too flat to be rolled easily

Tips of needles blunt or rounded, undersurface with 2 white bands; cones with long,

conspicuous, 3-lobed bracts

Tips of needles pointed

Tops of needles grooved; woody seed cones broadly oblong in outline

22b. Tops of needles with ridges; lacking in cones, instead having a red, fleshy, cuplike

seed covering

Cercis (redbud)

Platanus (sycamore)

Quercus (oak)

10

Comus (dogwood)

11

Eucalyptus (eucalyptus)

12

Arbutus (madrone)

13

Catanopsis (golden

chinquapin)

14

Lithocarpus (tanoak)

Salix (willow)

16

23

17

18

Pinus (pine)

Larix {larch)

Abies (fir)

19

Picea (spruce)

20

Tsuga {hemlock)

21

Pseudotsuga (Douglas fir)

22

Sequoia (redwood)

Taxus (yew)

Taxonomy: Classifying and Naming Organisms 235

23a. Twig ends appear as if jointed Calocedrus (incense cedar)

23b. Tips of branches flattened, not jointed in appearance 24

24a.

24b.

Leaves glossy and fragrant

Leaves awl-shaped, arranged spirally on twig

Thuja (Western red cedar)

Sequoiadendron (giant sequoia)

Glossary to Tree Key

• Acorn-The fruit of an oak, consisting of a nut and its basally attached cup (Figure 18-9d) • Acute-Sharp-pointed (Figure 18-2) • Alternate-Describing the arrangement of leaves or other structures that occur singly at successive nodes or

levels; not opposite or whorled (Figure 18-5) • Angiosperm-A flowering seed plant (e.g., bean plant, maple tree, grass) • Armed-Possessing thorns or spines • Asymmetrical-Not symmetrical • Axil-The upper angle between a branch or leaf and the stem from which it grows • Axillary bud-A bud occurring in the axil of a leaf (Figures 18-3 through 18-7) • Basal-At the base • Blade-The expanded, more or less flat portion of a leaf (Figure 18-2) • Bract-A much reduced leaf • Capsule-A dry fruit that splits open at maturity (e.g., buckeye; Figure 18-9e) • Compound leaf-Blade composed of two or more separate parts (leaflets) (Figures 18-4, 18-7) • Cordate-Heart-shaped (Figure 18-2) • Deciduous-Falling off at the end of a functional period (such as a growing season) • Drupe-Fleshy fruit containing a single hard stone that encloses the seed (e.g., cherry, peach, or dogwood;

Figure 18-9g) • Fruit-A ripened ovary, in some cases with associated floral parts (Figure 18-9a-g) • Glandular-Bearing secretory structures (glands) • Gymnosperm-Seed plant lacking flowers and fruits (e.g., pine tree) • Lateral-On or at the side (Figure 18-4) • Leaflet-One of the divisions of the blade of a compound leaf (Figures 18-4, 18-7) • Lobed-Separated by indentations (sinuses) into segments (lobes) larger than teeth (Figure 18-3b) • Node-Region on a stem where leaves or branches arise (Figures 18-2 through 18-7) • Nut-A hard, one-seeded fruit that does not split open at maturity (e.g., acorn; Figure 18-9d) • Obtuse-Blunt (Figure 18-6) • Opposite-Describing the arrangement of leaves of other structures that occur two at a node, each separated

from the other by half the circumference of the axis (Figure 18-6) • Palmately compound-With leaflets all arising at apex of petiole (Figure 18-7) • Petiole-Stalk of a leaf (Figures 18-2, 18-3, 18-4, 18-7) • Pinnately compound-A leaf constructed somewhat like a feather, with the leaflets arranged on both sides of

the rachis (Figure 18-4) • Pith-Internally, the centermost region of a stem (Figure 18-8a, b) • Pod-A dehiscent, dry fruit; a rather general term sometimes used when no other more specific term is

applicable (Figure 18-9£) • Fame-Fleshy fruit containing several seeds (e.g., apple or pear; Figure 18-9a) • Rachis-Central axis of a pinnately compound leaf (Figure 18-4) • Samara-Winged, one-seeded, dry fruit (e.g., ash fruits; Figure 18-9c) • Schizocarp-Dry fruit that splits at maturity into two one-seeded halves (Figure 18-9b) • Simple leaf-One with a single blade, not divided into leaflets (Figures 18-3, 18-5, 18-6) • Spine-Strong, stiff, sharp-pointed outgrowth on a stem or other organ (Figure 18-6) • Symmetrical-Capable of being divided longitudinally into similar halves • Terminal-Last in a series (Figure 18-4) • Thorn-Sharp, woody, spinelike outgrowth from the wood of a stem; usually a reduced, modified branch • Tooth-Small, sharp-pointed marginal lobe of a leaf (Figure 18-3a) • Truncate-Cut off squarely at end (Figure 18-3a) • Unarmed-Without thorns or spines • Whorl-A group of three or more leaves or other structures at a node

236 E X E R C I S E 1 8

18.3

Each year millions of" evergree:1" trees b ecome the center of attraction in human d wellings during the Christmas season . The process cf sel ecting the all-important tree is the same whether you resid e in the city w h er e you b u y your tree from a commercial grower, or w h ether you cu t on e off your " b ack forty." You ponder and evaluate each specimen until, with the u tmos t confiden ce, you bring home that perfect tree. Now that you h ave i t, just what kin d of tree stands i n you r h ome, l ook i n g som ewh at l i k e a cross b etween Old G l ory an d the Sis ti n e Chapel ? This key contains most of the trees that are u sed as Christmas trees; other gymnosperm trees are inclu ded, too. The common "Ch ris tmas trees" have an asterisk after th eir scientific name. Note that this key, unl ike those in the preceding section s, ind icates actual species d esi gnation s.

1a. Tree fragrant, boughs having supported (on clear moonlit nights) masses of glistening snow on their green needles; tree a product of nature

1 b. Tree not really a tree but rather a product of a cold and insensitive society; tree

2a.

2b.

3a.

3b.

4a.

4b.

5a.

5b.

6a .

6b.

?a.

never giving life and never having life

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

Leaves deciduous; for this reason not a desirable Christmas tree

Leaves in clusters of 2-5, their bases within a sheath

Leaves borne singly, not in clusters

Cones 1.25- 1.8 em long, 12-15 scales making up cone

Cones 1.8-3.5 em long, 40-50 scales comprising cone

Leaves 5 in a cluster, cones 1Q-25 em long

Leaves 2 in a cluster, cones less than 10 em long

Leaves 2.5-7.5 em long

Leaves 7.5-15 em long

Leaves with a bluish cast; cones with a stout stalk, pointing away from the tip of the branch ; bark orange in the upper part of the tree

?b. Leaves 1.25-3.75 em long; cones stalkless, pointing forward toward the tip

Sa .

of branch

Leaves slender, shiny; bark of trunk red -brown ; cones 5-7.5 em long ; scales of cones without any spine at tip

8b. Leaves thickened , dull ; bark of trunk gray to nearly black; cones 5 to 7.5 em long;

9a.

9b.

10a.

10b.

11 a.

11 b.

scales of cone armed with short spine at tip

Leaves scalelike or awl-shaped

Leaves needlelike

Twigs flattened , leaves all of one kind, scalelike, extending down the twig below the point of attachment

Twigs more or less circular in cross section ; leaves of two kinds, either scalelike or awl-shaped , often both on same branch , not extending down the twig ; coneless but may have a blue berrylike structure

Leaves with petioles

Leaves lacking petioles, leaf tip notched, needles longer than 1.25 em

2

17

3

4

5

9

Larix laricina (tamarack)

Larix decidua (larch)

Pinus strobus (white pine)

6

7

8

Pinus sylvestris * (scotch pine)

Pinus banksiana Uack pine)

Pinus resinosa * (red pine)

Pinus nigra * (Austrian pine)

10

11

Thuja occidentalis (white cedar, arbor vitae)

Juniperus virginiana (red cedar)

12

Abies balsamea* (balsam fir)

Taxonomy: Classifying and Naming Organisms 237

12a.

12b.

13a.

13b.

14a.

14b.

15a.

Leaves angular, 4-sided in cross section, harsh to the

touch; petiole adheres to twig

Leaves flattened

Leaves 3-10 mm long, blunt-pointed ; twigs rusty and hairy

Leaves 2 em long, sharp-pointed; twigs smooth

Cones 2.5-5 em long ; leaves ill-scented when bruised or

broken; smaller branches mostly horizontal

Cones 7.5-15 em long; scales comprising cone with

finely toothed markings; leaves not ill-scented when

bruised or broken; smaller branches drooping

Leaves pointed, over 1.25 em long; red fleshy, berrylike

structures present

15b. Leaves rounded at tip, less than 1.25 em long, with

two white lines on underside

16a.

16b.

17a.

17b.

Leaves 2-2.5 em long, dull dark green on top, with

two broad yellow bands on undersurface; petiole yellowish

Leaves 1.25-2 em long, without yellow bands

on underside

Tree a glittering mass of structural aluminum, sometimes

illuminated by multicolored floodlights

Tree green , made from petroleum products ;

used year after year; exactly like all others of its manufacture

238 E X E R C I S E 1 8

13

15

Picea mariana* (black

spruce)

14

Picea glauca * (white spruce)

Picea abies* (Norway spruce)

16

Tsuga canadensis (hemlock)

Taxus cuspidata (Japanese yew)

Taxus canadensis (American

yew)

Aluminous ersatzenbaum *

(aluminum substitute)

Plasticus perfectus * (plastic

substitute)

Name------------------ Sectio n Numbe r ____________ _

EXERCISE 1 8

Taxonomy: Classifying and Naming Organisms

Post-Lab Questions

Introduction

1. If you were to use a binomial system to identify the members of your fa mily or the family of a friend, (mother, fa ther, sis ters, bro thers), how would you write their names so that your system would most closely approxim a te that used to designate species?

G;aet\v~ rJ'~r..a,w;,· ...svl~ ~ ~pi+heJ-

SJ...a.w// flP<.-dlA-- uh.awir' lo / ()._ 2. Describe several advantages of using scientific names instead of common names.

• .:Sde.-n-\-\~-L Y)Q.me5 c::A.Y"e.... \.J.Sec~ -+\.-Y"ou_:J~c:llJ-\- \-he... LL;c-XlJ ~ v-d -\-~ ?r-<:""- un~9 ue_ .\-o ec:AC'-" \:::_; nd ~ o'l-3o..n\ s 'm, ,

c f>1-o!en-h- --t~<- trob\e.t'Yls ~nd ccnhAS:IC)h ~~ ~~c_ Cz\~ ~ c.a>vn mo 11 V\?'.ntCS ·

3. Based on the following classifica tion scheme, which two organisms are most closely phylogenetically related? Why?

Organism 1 Organism 2 Organism 3 Organism 4

Kingdom Animalia Animal ia An imalia Animalia

Phylum Arthopoda Arthropoda Arthropoda Arthropoda

Class Insecta Insecta Insecta Insecta

Order Coleoptera Coleoptera Coleoptera Coleoptera

Genus Cau/ophilus Sitophilus Latheticus Sitophilus

Specific epithet oryzae oryzae oryzae zea maize

Common name Broadnosed grain Rice weevil Long headed Maize weevil

weevil flour beetle

Taxonomy: Classifying and Naming Organisms 241

- ---- ------------------

I

18.2 Using a Taxonomic Key

Consider the drawing ofplants A and B in answering questions 4-6.

plant A plant B

4. Using the taxonomic key in the exercise, identify the two plants as either angiosperms or gymnosperms.

Plant A is a (an) An,8\cs~ms Plant B is a (an) qyvnrospermS

5. To what genus does plant A belong? What is its common name? genus: ______________________________________________________________________ _

common name: ______________________________________________________________________ _

, 6. To what genus does plant B belong? What is its common name?

genus:------------------------------------------------------~---------------

commonname: ______________________________________________________________________ _

Consider the drawing of plants C and Din answering questions 7-9.

242 £ X E R C I S E 1 8

7. As completely as possible, describe the leaf of plant C.

r~ve..s bra~d1 -....... -Ha-\; 5'VYlf>ltz--

8. To what genus does plant C belong? What is its common name? genus: ______________________________________________________________________ __

corrunonname: ______________________________________________________________________ __

9. Using the taxonomic key to freshwater organisms in the exercise, identify the genus of the organism below.

0 13

L---------------------------------------------------~~

genus: ______________________________________________________________________ __

Food for Thought

10. If you owned a large, varied music collection, how might you devise a key to keep track of all your different kinds of music?

Taxonomy: Classifying and Naming Organisms 243

Pre-Lab Questions

-- 1.

-- 2.

-- 3.

~ name "human" is an example of a common name. scientific name.

(c) binomial. (d) polynomial.

Current scientific thought places organisms in one of_ kingdoms. (a) two (b) four (c) five ® six

The scientific name for the ruffed grouse is Bonasa umbellus. Bonasa is 5£)l::ia) the family name. ® the genus. (c) the specific epithet. (d) all of the above

__ 4. A binomial is always a (a) genus. (b) specific epithet. (c) scientific name. @)) two-part name.

5. The science of classifying and naming organisms is known as ~ taxonomy. (b) phylogeny. (c) morphology. (d) physiology.

6. Which scientific name for the wolf is presented correctly? (a) Canis lupus (b) canis lupus ~ Canis lupus 'tO) Canis Lupus

7. A road that dichotomizes is (aj an intersection of two crossroads. ~a road that forks into two roads. (c) a road that has numerous entrances

and exits. (d) a road that leads nowhere.

8. Most scientific names are derived from (a) English.

(@) Latin. (c) Italian. (d) French.

9. One problem with using common names is that (a) many organisms may have the same

common name. (b) many common names may exist for

the same organism. (c) the common name may not be

familiar to an individual not speaking the language of the common name.

@ all of the above are true. 10. Phylogeny is the apparent

(a) name of an organism. @/ancestry of an organism. (c) nomenclature. (d) dichotomy of a system of

classification.

Taxonomy: Classifying and Naming Organisms 239

II

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