TAXONOMIC KEYS

 

 I. Introduction to identification

 

A. Mustard and flamingos.

    Let's start with a quote from Lewis Carroll's, Alice’s Adventure’s in

Wonderland:

 

          "Very true", said the Duchess: "Flamingos and mustard

          both bite. And the moral of that is – 'Birds of a

          feather flock together.'"

          "Only mustard isn’t a bird", Alice remarked.

          "Right as usual, said the Duchess: "what a clear way

          you have of putting things!"

          "It’s a mineral, I think," said Alice.

          "Of course it is" said the Duchess, who seemed ready to

          agree to everything Alice said: "there’s a large

          mustard-mine near here. And the moral of that is – 'The

          more there is of mine, the less there is of yours!'"

          "Oh, I know!" exclaimed Alice, who had not attended to

          this last remark, "it’s a vegetable. It doesn’t look

          like one, but it is".

 

B. The need for identification.

    We share the planet with at least 1.5 million (some estimates are as

high 30 million) other species. In order to communicate, retrieve, store,

and accumulate information about our co-inhabitants, it has been necessary

for biologists and others to: (1) identify these organisms; (2) name them;

and (3) place the organisms into groups that reflect our current knowledge

of their evolutionary relationships. As we know, collectively these

activities - identification, nomenclature and classification - make up the

discipline of taxonomy. Here we'll focus here on identification.

 

II. Identification.

    Suppose that you didn't know that the large bird Alice is carrying is a

flamingo. How could you identify this creature that "bites"? The answer is

simple in theory - we would compare the "mystery bird " to other "known" or

"reference" or "type" birds until we find one that matches. If, after an

exhaustive search, we don't find a match we may be studying a species new

to science. The process of matching a mystery organism to known ones can be

accomplished by:

 

          A. Asking an expert.

              Consult an individual who has spent his/her life

          studying birds (ornithologist). This method usually

          provides a reliable and accurate answer because it is

          based on the wisdom and years of experience of a

          professional. "Experts" are typically found in

          botanical gardens, museums, herbaria, colleges,

          universities, etc. Unfortunately, experts are not

          always available (or willing) to help, so you must be

          prepared to do your own identifications. Note, it is

          common even for professional taxonomists to send

          "difficult" specimens to experts.

 

          B. Hunting-and-Pecking.

              In this case, we search through a field guide,

          museum or zoo for a bird that matches our mystery bird.

          Although we may get lucky, this method is the least

          satisfactory because of the small probability that we

          will stumble upon the match. This can be time-consuming

          and is not very efficient. Picture books are designed

          for hunting-and-pecking.

 

          C. Using a taxonomic key.

              A key is a device, which when properly constructed

          and used, enables a user to identify an organism. There

          are two types of keys that we will discuss; (a)

          dichotomous and (b) polyclave (also called multiple

          access or synoptic).

 

III. Dichotomous keys.

    (di - two; chotomy - forked). These keys, which are the most common,

were probably first published by Jean Baptiste-Lamarck in 1778 (remember

him, Mr. Acquired Traits?). They consist of a series of paired statements,

termed couplets, that describe some feature of the organism. The

statements, or leads, are in direct contrast (i.e., mutually exclusive). To

use the key, begin with the first couplet and select the statement that

best fits your specimen. This will direct you to another couplet and

ultimately provide the identity of your specimen.

 

A. Types.

    There are two types of dichotomous keys. They differ in the method by

which the couplets are organized and how the user is directed to successive

choices.

 

       1. Indented Keys (also called yoked) - indents the choices (leads)

          of the couplet an equal distance from the left margin. The two

          choices of the couplet are usually labeled 1 and 1' or 1a and 1b.

          It is not necessary that the choices are numbered, but it helps.

          The user goes to the next indented couplet following the lead

          that was selected. For an example, check out Figure 1.

       2. Bracketed keys - provides both choices side-by-side. The choices

          of the couplet must be numbered (or lettered). It is very helpful

          if the previous couplet is given. Note: in some bracketed keys

          alternate couplets are indented; in others, all couplets begin at

          the left margin. The user proceeds to the couplet that is

          indicated by the lead selected.  For an example, check out Figure

          2.

       3. Examples of both types of keys will be shown in class. In

          general, botanists prefer indented keys. Advantages of indented

          keys include: (a) similar specimens are grouped together; (b) it

          is harder to get lost or loose your place; (c) they are faster to

          use; and (d) it is easier to retrace your steps if you make a

          "wrong turn". Which kind is used in our texts? Which type do you

          prefer? Why?

 

B. Using a dichotomous key.

    To demonstrate how a key works we will identify some of the creatures

(i.e., Flamingo, Gryphon, Mock turtle, Cheshire Cat, Dormouse) from Lewis

Carroll (see Figures 1 and 2). Tips for using a key:

 

  1. don't guess - be sure that you understand the meaning of any terms

     that are used in the key;

  2. read both choices;

  3. measure;

  4. watch for "weird" (abnormal) specimens and remember the natural

     variability in all organisms;

  5. when in doubt, try both choices;

  6. check your answer with a description or photo or herbarium specimen.

 

C. Problems using dichotomous keys.

    Aside from being poorly written (see below), a key may be difficult to

use because:

 

       1. the key doesn't include all potential variations in the species;

       2. the key relies on features not present in that season;

       3. the key doesn't include "all" species of interest;

       4. you misinterpret a feature or make a mistake.

 

All of these mistakes can lead to frustration. But, try, try again!

 

D. Writing a dichotomous key.

    First collect your data by: (a) laying out the plants to be keyed in

front of you; and/or (b) recording data on note cards or in a computer

spreadsheet or database; and/or (c) creating a table listing the species to

key along one side and the characters to study along the other side (See

Table 1 for the data used to created the keys to Lewis Carroll's

creatures). Once you have collected your data, start to group the objects.

It is best to start with a feature that separates the things to be keyed

into two groups of similar number and then subdivide these groups until

individuals are distinguished.

 

Other tips for key writing:

 

   * start each couplet with a noun;

   * avoid unnecessary words;

   * avoid negatives;

   * avoid trichotomies;

   * use "absent" vs. "not present";

   * quantify;

   * the two statements of couplet should refer to the same feature;

   * each couplet should include all of the potential variations in the

     feature;

   * the two statements of the couplet should be mutually exclusive;

   * remember that keys are for identification and are not designed to show

     evolutionary relationships (i.e., keys are "artificial") - thus, don't

     worry about maintaining "natural" groupings;

   * avoid vague terms;

   * season of use should be consistent within the key;

   * don't include taxonomic names (i.e., plant a gymnosperm);

   * use obvious features, avoid obscure or highly technical ones;

   * use fixed features, avoid variable ones;

   * start each couplet with the noun; and

   * start with the most distinctive features.

 

The finished key should have n-1 couplets (where n equals the number of

units in the key).

 

Figure 1:  Bracketed Key to Some Characters from the "Alice" stories by

Lewis Carroll

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1a.      Wings present ..................................2

1b.      Wings absent ...................................3

 

2a (1)   Body covered only with feathers............Flamingo

2b.      Body covered with feathers and fur........Gryphon

 

3a. (1)  Fur absent, animal usually crying...........Mock Turtle

3b.      Fur present, animal rarely crys.............4

 

4a. (3)  Able to disappear, usually with a grin......Cheshire Cat

4b.      Unable to disappear, usually asleep........Dormouse

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Figure 2:  Indented Key to Some Characters from the "Alice" stories by

Lewis Carroll

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1a.     Wings present

                2a.      Body covered only with features........Flamingo

                2b.      Body covered with feathers and fur...Gryphon

1b.     Wings absent

                3a.      Fur absent, animal usually crying........Mock

Turtle

                3b.      Fur present, animal rarely crys

                              4a.   Able to disappear, with a

grin.......Cheshire Cat

                               4b. Unable to disappear, usually

asleep...Dormouse

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                    Characters/States

   Taxon

            Wings   Fur   Unique Behavior(s)

 Cheshire

 Cat        absent   +  disappears, grins

 Dormouse   absent   +  usually asleep

 Gryphon   present   +

 Flamingo  present   -

 Mock

 Turtle     absent   -  usually crying

 

IV. Polyclave/Random Access/Synoptic Keys.

 

A. General.

    Another type of key is termed multiple access or polyclave or synoptic

key. The advantage of these keys is that they allow the user to enter the

key at any point. These keys are a relatively new alternative to

dichotomous keys and are becoming increasingly popular, especially because

of the ease of computerizing them.

 

    Identifying organisms with a polyclave is a process of elimination. In

a written polyclave key there is a series of characters and character

states. Each state is followed by a number or code for the species that

possess that feature. The user selects any character and then copies down

the list of species that possess the feature. Then the user selects another

character and eliminates any species not common to both lists. This process

continues until the specimen is identified.

 

    It's easy to imagine how these keys are computerized. Consider a series

of standard playing cards. Imagine each card has four holes punched into it

along the top margin. If the card is a spade we cut the first hole through

to the margin; if a club, the second hole is notched to the margin; a heart

the third hole is notched; and finally if it is a diamond the fourth hole

is notched. Further imagine that along the bottom of the card we punch 14

holes (2 - 10, J, K, Q, A) and cut a notch for the appropriate number.

Thus, the Queen of Hearts will have a notch cut into the third hole on the

top of the card, and the Queen notch on the bottom of the card.

 

    Now, let's use our punch card deck of cards to identify an unknown

card. Shuffle another deck of cards and pick any card. Let's assume that

this "unknown" card is the Ace of Spades. To identify this unknown, we

analyze the characters and two are obvious, suit and number. Let's start

with suit - take a long needle and stick it through the "spades hole".

Since, only spades are notched, the other suits will remain on the needle

and spades will drop out of the deck. Cool. Now, collect the spades cards

and put a needle through the next character, the Ace. And, viola, the Ace

of Spades falls out. This is the general principle of how the computerized

version of polyclave keys work. The main difference is that a computer

allows for countless holes (characters) and notches (states) to be included

and does the needlework for us.

 

B. Advantages.

    The advantages of a polyclave (multiple-access) key are:

 

       1. easy to use;

       2. multi-entry - meaning the user can start anywhere. This is a

          significant advantage because the user can rely on characters

          that are most easy to observe, rather than having to deal with

          characters that may not be present in the specimen or are poorly

          developed;

       3. order-free - meaning the user can work in any direction with any

          character;

       4. faster; and

       5. easily computerized. In fact, these keys are most commonly used

          in this form. Paper versions are typically large and unwieldy

          because each character needs to list all possible taxa.

 

C. Example.

    An example of a "paper version" of a synoptic key to pollination

systems follows. To use this key: (1) Read through the list of characters

to become familiar with the possibilities; (2) Scan the list to find a

character with a state that you observe in your specimen. Start with a

readily identifiable character that has only a few numbers (taxa)

associated with it; (3) Write a brief description of the character and

state and the numbers of the taxa that can be described by this state; (4)

Choose another character and state that describes your taxa. Write a brief

description of this state below the name of the first state chosen. Then,

scratch off the original list any taxon that doesn't appear in the second;

(5) Continue this process until just one taxon remains for all of the

states. If there is no single taxon described by the states chosen, and two

or more remain, go back and check for errors; (6) Read the name of the

taxon after its number in the list of taxa. Check your identification with

a description in a manual or the herbarium.

 

    There are several computer programs for preparing synoptic keys

including PCTaxon and the XID authoring system. Follow the directions for

use of these keys.

 

References:

 

   * Glasenapp, D. J. 1986. The nuts and bolts of classification. American

     Biology Teacher 48: 362-3.

   * Harrington, H.D. 1957. How to Identify Plants. Swallow Press, Chicago.

 

Web Sites:

 

   * Interactive Keys - MJ Dallwitz

   * Comparison of interactive Keys - MJ Dallowitz

 

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                     Polyclave Key to Pollination Type

 

    Pollination is the process of transferring pollen from one flower to

another. Since plant can't move, they utilize vectors such as wind, water

and animals to accomplish this process for them. Flowers are specialized by

shape, color, odor, nectar reward in order to maximize the chance that a

certain vector will accomplish pollination. These flower adaptations are

collectively known as pollination syndromes or systems.

 

    Plants differ in the degree of their specialization for a particular

pollination system. For example, many orchids are pollinated by only a

single type of bee. Other flowers are not as specialized and may be

pollinated by a variety of bees or perhaps beetles. In other cases, insects

may visit flowers without actually transferring pollen. These factors make

it difficult to determine with absolute certainty the pollination system by

the polyclave key.

 

    To illustrate how to use a polyclave key, let's determine the

pollination system of a dandelion.

 

GENERAL DIRECTIONS DANDELION EXAMPLE

 

1.   Select   any  one   of  the   FLOWER

CHARACTERS  in  the  key. Note:  you  can

choose   the  characters  in  any   orderLet's choose FLOWER COLOR

(i.e., multi  - entry)

2. Choose the character state

(description)  that  matches  the  flowerDandelions are Yellow

you are observing

3.  Write down  the possible  pollination

systems for this feature                 BE,BU,BI

4. Select another feature                NECTAR

5. Choose the character state

description   that  matches  your  flowerb. present...WI,FM,BE,BA

6.  Eliminate  from the  first  character

state  selected  the pollination  systems

not  found on  both lists. Continue  thisBE,BU,BI

process  until the pollination system  isThus, dandelions are bee

identified.  Note: in some cases  it willpollinated

not  be possible to narrow the choices to

just one.

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                   Polyclave Key to Pollination Systems.

 

    (Adapted from Tyrell, L. 1989. Journal College Science Teaching, May

                                  378-383)

 

FLOWER SYMMETRY

 

     a. radial ....... WI,BT,FM,FS,BE,BU,MO,BI,BA

     b. bilateral .............. WI,BE,(BU),BI,BA

 

FLOWER SHAPE

 

     a. tubular ............... FS,BE,BU,MO,BI,BA

     b. not tubular .....BI,BT,FM,FS,BE,(BU),(BI)

 

FLOWER SIZE

 

     a. small/inconspicuous ............ WI,FM,FS

     b.  showy, large,  conspicuous, or  small in a  conspicuous group

     .......BT,(FM),FS,BE,BU,MO,BI,BA

 

FLOWER COLOR

 

     a. white .......... BT,FM,(BE),BU,MO,(BI),BA

     b. yellow ......................... BE,BU,BI

     c. blue ................. BT,BE,BU,(MO),(BI)

     d. red ......................(BE),BU,(MO),BI

     e. dull or dark ..... WI,BT,FM,FS,MO,(BI),BA

 

WHEN FLOWER IS OPEN

 

     a. night only ...WI,BT,FM,FS,(BE),(BU),MO,BA

     b. day only ...... WI,BT,FM,FS,BE,BU,(MO),BI

     c. day and night..WI,BT,FM,FS,BE,BU,MO,BI,BA

 

ODOR

 

     a. no odor ............... WI,BT,FM,BE,BU,BI

     b. putrid ................... BT,FM,FS,BE,BU

     c. fragrant .............. BT,FM,BE,BU,MO,BA

 

POLLEN

 

     a. few grains ......... BT,FM,FS,BE,BU,MO,BI

     b. abundant ..... WI,BT,FM,FS,BE,BU,MO,BI,BA

 

NECTAR

 

     a. none ........................ WI,BT,FM,FS

     b. present...................... WI,FM,BE,BA

 

NECTAR GUIDES*

 

     a. present .......................... BE,BU

     b. absent ............ WI,BT,FM,FS,MO,BI,BA

 

NECTAR CONTENT**

 

     a. low sugar............. WI,BT,FM,FS,BU,MO

     b. low amino acids ....WI,BT,FM,FS,BE,BI,BA

 

________________________________________________________________

 

*  May   only  appear  under  UV  light  **   Taste  can  provide  a  clue.

 

 

 

Abbreviation Code:

 

WI Wind pollination (anemophily); BT Beetle pollination (cantharophily); FM

Fly pollination (syrphid and bee flies; myophily); FS Fly pollination

(carrion and dung flies; sapromyophily); BE Bee pollination

(mellittophily); BU Butterfly pollination ; (psychophily); MO Moth

pollination (phalaenophily & sphingophily); BI Bird pollination

(ornithophily); BA Bat pollination (chiropterophily)

 

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Some Exercises:

 

1. You will be given a set of "sham" plants created by Dr. Warren Wagner,

University of Michigan. Study these plants. Select 10 different characters

and record the state for each character in the table. Then, use this table

to prepare a dichotomous key, either indented or bracketed, to these

species. Can you rewrite your key in the other form?

 

2. For additional practice, prepare a dichotomous key (bracketed or

indented) to one of the following sets of terms (or make up your own set of

terms):

 

   * Special modifications - tendril, thorn, spine, prickle

   * Leaf shape - linear, oblong, lanceolate, ovate, elliptic, orbicular,

     reniform

   * Leaf bases/apex - acute, acuminate, obtuse, rounded, truncate,

     cordate, oblique, hastate, sagittate, peltate

   * Leaf margins - entire, crenate, serrate, doubly serrate, dentate,

     lobed

   * Surface features - glabrous, pubescent, pilose, hirsute, scabrous,

     tomentose, glaucous

   * Bud terminology - bud scale, bud scale scar, stipule scar, leaf scar,

     vascular bundle scar

   * Leaf attachment - basal, cauline, alternate, opposite, whorled

   * Leaf attachment - petiolate, sessile, perfoliate, clasping, sheathing

   * Stem types - rhizome, stolon, corm, bulb, tuber

 

3. Prepare a dichotomous key to some of your plants-to-know.

 

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