BASICS: CLASSIFICATION, NOMENCLATURE, AND KEY MAKING
for this section are to learn:
- the differences between classification, nomenclature, and
- the definition of : circumscription, rank, taxa, taxon,
dichotomous, key, character, couplet
- the ranked hierarchy used in flowering plant classification
and the associated word endings
- how to write and interpret species names, including the
- the characteristics of a well-written dichotomous key
The parts of today's lesson are
1. Two views on taxonomy
2. Uses of taxonomy
Useful because if you know about a group, you can know about an
plant that is a member of the group. Conversely, if you know a member
two of a group, you can make some good guesses about the group as a
Categories can be ordered by inclusiveness. More inclusive categories
have higher ranks and less inclusive categories have lower
As we go down this list, the categories become less inclusiveand
of lower rank:
**Plant categories can be arranged the same way.
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
in which a new condition is added at each step:
Things with wheels = buses, cars, bicycles, skates, airplanes, trains,
**The KEY CHARACTERS, the features used to CIRCUMSCRIBE the
must be presented so that they mean the same thing to everyone.
And is ground transport = buses, cars, bicycles, trains
And can carry more than one person = buses, cars, trains
And runs on rails = trains
II. HOW ALL THIS APPLIES TO PLANTS--
A. The system--
Each category has its own basis for circumscription, and each
of rank) is a taxon (pl., taxa)
B. Example #1--
Plantae--includes all plants
**The name for a species consists of the genus name and the
Magnoliidae--subclass for Magnolia-like plants
Magnoliales--order for Magnolia-like plants
Magnoliaceae--family for Magnolia-like plants
Magnolia--genus that includes all
**Notice that the endings will always tell you what rank you
dealing with, even if you don't recognize the word. For example,
word "Sterculiaceae" could only refer to a family.
**As you go up, each category is made of groups of members of
category below it--e.g., there are many types of Magnolia but they
all fit into the genus Magnolia. The Magnolias and their
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
something that (usually) exemplifies the circumscription of that
There are many families in the Magnoliales, for example, but the
best typifies what the order is supposed to be like, so it is called
**The above is an example of an important genus that has
named for it all the way up.
C. Example #2--(bottom up, this time)
Winecup, a species of Callirhoe
Malvaceae--family named for some other genus
There will be other genera besides Callirhoe in the Malvaceae,
Malva, for which the family is named. Likewise, there are other
besides the Malvaceae in the Malvales.
Malvales--order named for the family
Dilleniidae--subclass named for some other family
Magnoliopsida--still a dicot
Magnoliophyta--still a flowering plant
*In this course our plants will come from several subclasses and
classes (monocots and dicots), but they will all belong to the
NOW RELAX! YOU DON'T HAVE TO THINK ABOUT THIS ALL AT ONCE!
A plant needs a name that applies to it and only to it, and
which means the same thing to everyone.
B. The formula--
Callirhoe involucrata (Torr.) Gray
--Callirhoe is the genus name. Genus names are
capitalized and underlined.
--involucrata is the specific epithet.
e.'s are underlined, but not capitalized. The sp. e. often
a character or a place of origin, etc.
--(Torr.) Gray is the authority, the
work(s) you would consult to find out why a plant is named and
as it is. In this case, (Torr.) indicates the plant's first
indicates the person responsible for placing the plant in its current
** Isn't it nice there are books to look all of this up in! **
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!
A series of choices in couplets that will lead the user to the
proper identification for a plant.
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.
Break your plants into ever smaller groups. Don't remove just one plant
at a time unless you have to.
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--
rather than isn't. Also notice the numbers in parentheses after
the couplet number. These indicate the couplet that sent you to the
couplet. Using these, you can backtrack if you make a mistake.
**Different keys use different combinations of indenting, letters,
bracketing, and typefaces. Get to know the keys you will be working
NOW: The TA may have the students develop a key to identify
Stress good, constant characters. Test run a few students through the
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 28 FJanuary
2010 by MDR