University of Saskatchewan: Virtual Herbarium


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What is Taxonomy?

Taxonomy is the classification of organisms into different categories based on their characteristics. In the eighteenth century, Carl Linnaeus developed the Linnaean system of classification that is an ordered way of grouping similar organisms. The current classification system works kind of like a pyramid. All living things are at the top of the pyramid then there are various categories under each division.

Taxonomic Classifications

Kingdom Plant
    Division Spermatophyta
       Class Gymnospermae
          Order Coniferales
             Family Pinaceae
                Genus Pinus
                   Species strobus

Using a Dichotomous Key

The dichotomous key is used for identifying unknown specimen.

A dichotomous key is made up of a series of couplets, each consisting of two separate statements. Start with the first couplet in the key and decide which statement describes the specimen you are trying to identify. For example:

Couplet #1
1. Floral parts in 4's or 5's; leaves net-veined; woody or herbaceous . . . 2 (go to couplet "2")
1. Floral parts in 3's or multiples of 3's; leaves usually parallel-veined; herbaceous . . . 30 (go to couplet "30")

Couplet #2
2. Flowers with only one floral ring (sepals OR petals) . . . 3
2. Flowers with two floral rings (sepals AND petals) . . . 5

3. Herbs . . . 4
3. Climbing shrubs . . . Ranunculaceae (Clematis), p. 362 fruit

4. Plants with stipules; fruit in a capsule . . . Caryophyllaceae (Paronychia), p. 347
4. Plants lacking stipules; fruits achenes or follicles . . . Ranunculaceae, p. 362
(The plant you are identifying belongs to the family Ranunculaceae. Continue narrowing this down to the specific plant name by going to page 362 in Flora of Alberta)

At the end of each line is information directing you to the next decision point. The information at the end of a line could be a couplet number, a page number or the name of a division, class, order, or family.

In the example above, if you choose the first statement in couplet #1, your next step is to go to couplet #2. If you choose the second statement in couplet #1, your next step is to go to couplet #30.

By choosing one of the two statements in each couplet, you progress through the key from broad characteristics to narrower characteristics until only a single choice remains. As long as the correct statement is chosen at each step along the way, and the unknown specimen is included in the key, a confident identification will be made.

If you get to the end of the process and the plant you find in the key does not match the specimen, it means that you made an error somewhere along the way. Go back and check each choice you made. To assist you, glossary terms appear as hyperlinks. If you are unsure what a term means, you can go to the glossary and check the meaning before you choose a statement from the couplet presented.