Unit B

Module 3 ~ Lesson 5

 Dichotomous Keys

Parks Canada employees must be able to distinguish between different organisms based on observations. For example,  wildflowers are not to be picked in the parks; however, Parks personnel can sometimes be seen pulling flowers in ditches. They are trained to be able to identify native species from invasive species. The native lance leaf aster and its invasive look alike, ox-eye daisy, are shown below.

Lance leaf aster

By Лобачев Владимир [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], from Wikimedia Commons

Ox-eye daisy

MabelAmber. Public Domain, via Pixabay.

Species classification is done using characteristics based on 
morphology to identify organisms. One way to identify different species is to use a dichotomous key. A dichotomous key is a series of questions that lead to the identification of a species. Questions in a dichotomous key refer to observable characteristics that can be used to identify an organism at the genus species level. This is the italicized Latin name that is recognized by scientists worldwide.


Read "Dichotomous Keys" on page 89 of your textbook.

 Using a Dichotomous Key

The best way to learn how to use a dichotomous key is to practice. 
  1. Practice using this electronic dichotomous key.
  2. Use an electronic dichotomous key to identify invertebrates found in a stream sample. The invertebrates in rivers, lakes, and streams are a good indicator of the water quality. More sensitive organisms will disappear first when the water begins to get polluted. As the water becomes more polluted, fewer types of organisms are able to survive. Healthy rivers and lakes will still contain the most sensitive macroinvertebrates.