BASICS: CLASSIFICATION, NOMENCLATURE, AND KEY MAKING

The parts of today's lesson are

Taxonomy
Classification
Nomenclature
and Keys

Colored text indicates a link to related or supplementary material.  
 

Taxonomy

1. Two views on taxonomy

a. There is order in the world if we can discover it.

b. There is chaos in the world; we can apply an artificial order system to it.

2. Uses of taxonomy

Useful because if you know about a group, you can know about an unfamiliar plant that is a member of the group. Conversely, if you know a member or two of a group, you can make some good guesses about the group as a whole.

I. INTRODUCTION

A. Classification--

Sorting things into categories. Categories can be grouped into larger groups, and so on.
Ex: M&M's, Hershey's kisses, jelly beans , and gumdrops are all different types of candy. M&M's and Hershey's kisses can be put in the category "Chocolate Candy", and the jellybeans and gumdrops might be put into a category labelled "Fruit-flavored Candy

The categories "Chocolate Candy" and "Fruit-flavored Candy", in turn, both fit into the broader category "Candy".

**The more things you let a category include, the less concrete it becomes. Eventually, you have a category labelled "stuff".

B. Rank--

Categories can be ordered by inclusiveness. More inclusive categories have higher ranks and less inclusive categories have lower ranks. As we go down this list, the categories become less inclusiveand of lower rank:
People
Americans
Texans
Aggies
     BOTN 301 students
 
**Plant categories can be arranged the same way.

C. Circumscription--

What do you use to define your categories? How do you set up a category so that it includes only what you want it to? Look at the following example in which a new condition is added at each step:
Things with wheels = buses, cars, bicycles, skates, airplanes, trains, etc.
And is ground transport = buses, cars, bicycles, trains
And can carry more than one person = buses, cars, trains
And runs on rails = trains
**The KEY CHARACTERS, the features used to CIRCUMSCRIBE the categories, must be presented so that they mean the same thing to everyone.

II. HOW ALL THIS APPLIES TO PLANTS--

A. The system--

Each category has its own basis for circumscription, and each (regardless of rank) is a taxon (pl., taxa)
Kingdom
Division
Class
Subclass
Order
Family
Genus
Species

B. Example #1--

Plantae--includes all plants
Magnoliophyta--flowering plants
Magnoliopsida--dicots
Magnoliidae--subclass for Magnolia-like plants
Magnoliales--order for Magnolia-like plants
Magnoliaceae--family for Magnolia-like plants
Magnolia--genus that includes all Magnolias
grandiflora--specific epithet
**The name for a species consists of the genus name and the specific epithet.

**Notice that the endings will always tell you what rank you are dealing with, even if you don't recognize the word. For example, the word "Sterculiaceae" could only refer to a family.

**As you go up, each category is made of groups of members of the category below it--e.g., there are many types of Magnolia but they all fit into the genus Magnolia. The Magnolias and their relatives are all in the Magnoliaceae. Orders are made up of families, subclasses are made of orders, etc.

**From family on up, categories are named after a typical member, something that (usually) exemplifies the circumscription of that category. There are many families in the Magnoliales, for example, but the Magnoliaceae best typifies what the order is supposed to be like, so it is called Magnoliales.

**The above is an example of an important genus that has categories named for it all the way up.

C. Example #2--(bottom up, this time)

Callirhoe involucrata--a Winecup, a species of Callirhoe
Malvaceae--family named for some other genus
Malvales--order named for the family
Dilleniidae--subclass named for some other family
Magnoliopsida--still a dicot
Magnoliophyta--still a flowering plant
Plantae--still a plant
There will be other genera besides Callirhoe in the Malvaceae, notably Malva, for which the family is named. Likewise, there are other families besides the Malvaceae in the Malvales.

*In this course our plants will come from several subclasses and two classes (monocots and dicots), but they will all belong to the Magnoliophyta--the flowering plants.

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NOW RELAX! YOU DON'T HAVE TO THINK ABOUT THIS ALL AT ONCE!

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III. NOMENCLATURE--

A. General--

A plant needs a name that applies to it and only to it, and which means the same thing to everyone.

B. The formula--

1. The genus name tells a plant's closest relatives.
2. The specific epithet tells which species it is.
3. The authority tells who first described the plant.

** Genus name + specific epithet = species name **

C. Example

--Callirhoe is the genus name. Genus names are capitalized and underlined.

 --involucrata is the specific epithet. Sp. e.'s are underlined, but not capitalized. The sp. e. often indicates a character or a place of origin, etc.

 --(Torr.) Gray is the authority, the person(s) whose work(s) you would consult to find out why a plant is named and classified as it is. In this case, (Torr.) indicates the plant's first describer. Gray indicates the person responsible for placing the plant in its current classification.

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** Isn't it nice there are books to look all of this up in! **

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IV. KEYS

A. Purpose--

Once you've described a plant, classified it, and given it a name, can you arrange some system so that someone else can use your knowledge without memorizing all the names and relationships involved?  
 

Yes, you can! It's called a KEY! TA DA!

B. Definition--

A series of choices in couplets that will lead the user to the proper identification for a plant.

C. Guidelines--

1. Only two choices presented at each step
2. Concrete characters used. e.g., "little" is not a good character.
3. Use the same lead word or words for each half of the couplet.
4. Words used must mean the same to all readers.

D. Strategy--

Break your plants into ever smaller groups. Don't remove just one plant at a time unless you have to.

E. Example--

1. Candy is chocolate.................................................2
1. Candy is not chocolate but fruity.............................3

2(1) Candy has colored coating...........................M&M
2. Candy has a foil wrapper............................Hershey's

3(1) Surface is sugar-covered; blob-shape........Gumdrop
3. Surface is smooth; bean-shape......................Jellybean

**Notice that the first choice in a couplet is positive-- something is rather than isn't. Also notice the numbers in parentheses after the couplet number. These indicate the couplet that sent you to the current couplet. Using these, you can backtrack if you make a mistake.

**Different keys use different combinations of indenting, letters, numbers, bracketing, and typefaces. Get to know the keys you will be working with in class.

Continue with the Exercise in Basic Taxonomy
Go back to the Table of Contents for the lab
Return to the Botany 301 homepage

last updated 9 January 2004 by MDR