Plant Taxonomy and
How to Identify Plants

Horticulture and the Science of Plants
  Horticulture Youth Adventure Program

David Wm. Reed, Instructor

Department of Horticultural Sciences
Texas A&M University


BACKGROUND

What is a Scientific Names and How are Plants Given Scientific Names
Plants are given scientific names based on the binomial system of nomenclature developed by Linnaeus in the late 1700's.  Each plant is given a scientific name. The scientific name is often called the Latin name because it is written in Latin.  The scientific name is  composed of two parts:  1) the genus name, and 2) the species name.  The  first person to identify a new plant has right to  give it  its scientific name.

How to Write a Scientific Name
The genus and species name are always written in italics or underlined.  The first letter of the genus is always capitalized.  The species is not capitalized, unless it is named after a proper noun. The scientific name is always written and pronounced the same, regardless of the language written or spoken.  An example of  the proper way to write a scientific name is as follows:

Sansevieria trifasciata or Sansevieria trifasciata 

How are Plants Given Common Names
Many plants are referred to by common names.  There are no rules for assigning common names to plants.  The problem with common names is that one plant may have many  common names, and they often are regional.  In addition, two different plants may have the same common name.  For example Sansevieria trifasciata has the common names of Snake Plant, Mother-in-Law's Tongue, Lucky Plant, or Bow-String Hemp.  Conversely, the common name Fan Palm is used for up to eleven separate species of palms. 

Keys
A key is a tool for identifying an unknown plant species.  Dichotomous (forking) keys are usually used for identifying plants.  The key is composed of successive choices between two contrasting statements called couplets.  The couplets are usually denoted by the same number or level of indentation.  With a representative plant sample in hand, one completely reads the two contrasting statements (couplet) and then chooses the correct, or most correct, statement.  The correct statement will instruct you to proceed to the next couplet where you again choose the most correct statement.  This process is followed until a couplet is reached where the correct statement lists the name of the unknown plant. This is analogous to traveling down a many forked road.  To get to the final destination, the correct choice must be made at each fork.

Keep in mind the following points when using keys:

1)   Read BOTH contrasting statements (couplet) completely. Even if the first choice sounds correct, the second may be more correct.

2)   If a term is unfamiliar, look up its definition - DO NOT GUESS!

3)   Make measurements with a ruler - DO NOT GUESS!

4)   Nature is highly variable, look at several samples before deciding.  NEVER rely on just one sample.

5)   If in doubt about a choice, follow it both ways, then choose between the final choices.

TAKE HOME LESSONS
1) To learn what a is a scientific name.
2) To learn how to write a scientific name.
3) To learn how to use a key to identify the name of a plant.
4) To learn how to make a key.

MATERIALS NEEDED
Sansevieria to key out.
A bag of various kinds and shapes of leaves and stems to use to make a key.

PROCEDURES
Scientific names
The class will practice writing scientific names.

How to use a key to identify the name of a plant.
The class will use the Key to Sansevieria to key-out and identify the name of several Sansevieria species.

How to make a Key
The students will break up into groups of 3.  Your instructor will supply you with a bag containing a dozen or so different kinds of plants.  Working in groups of 3-4, you are to construct a key that can be used to identify the samples.  Constructing your own key is an excellent way of learning how to use them and learning the disadvantages or pitfalls of using keys.  The following guidelines will be helpful in constructing the key.

1)   Study the key to Sansevieria to become familiar with the physical layout and numbering system.  These are called indented keys.  Each statement of the couplet is preceded by the same number and/or is at the same level of indentation, and may be physically separated.  Each statement of the couplet either identifies the unknown or leads to another couplet until the statement ends in a name.

2)   The key must be based on constant characteristics if it is to be useful.  To start the key, separate the plant samples into two piles based on the highest characteristic (i.e. leaves needle or scale-like vs. leaves broad), then separate each pile based on another distinquishing characteristic.  Write the key based on these statements used to separate the piles..

3)   Start the contrasting statements of each couplet with the same word (capitalize only the first word), preferably a noun followed by adjectives.  For example:

1)   Leaves needle-like or scale-like

1)   Leaves broad

4)   When you have separated a  plant into a 1-plant pile, then write the plant name at the end of the line.


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