Dichotomous Key Archives - Eva Varga

May 1, 201410

Systema Naturae was one of the major works of the Swedish botanist, zoologist and physician Carolus Linnaeus. Although the system, now known as the binomial naming system, was partially developed by Gaspard and Johann Bauhin, 200 years earlier, Linnaeus was first to use it consistently throughout his work.

binomial naming systemHe first published Systema Naturae in 1735. However, it is the 10th edition that is the most important and is considered to be the starting point of zoological nomenclature; the full title of which was, Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis or translated: “System of nature through the three kingdoms of nature, according to classes, orders, genera and species, with characters, differences, synonyms, places”.



Carolus Linnaeus (23 May 1707 – 10 January 1778) was a Swedish naturalist and physician. His botanical work Systema Naturae in 1758 contained his system for classifying plants into groups depending on the number of stamens in their flowers, providing a much-needed framework for identification. He also devised the concise and precise system for naming plants and animals, using one Latin (or Latinized) word to represent the genus and a second to distinguish the species; a system that has become known as the binomial naming system.

Linnaeus was born in the countryside of southern Sweden. He received most of his higher education at Uppsala University, and began giving lectures in botany in 1730. He livedabroad from several years in the 1730s, where he studied and also published a first edition of his Systema Naturae in the Netherlands. He then returned to Sweden, where he became professor of medicine and botany at Uppsala.

In the 1740s, he was sent on several journeys through Sweden to find and classify plants and animals. In the 1750s and ’60s, he continued to collect and classify animals, plants, and minerals, and published several volumes. At the time of his death, he was one of the most acclaimed scientists in Europe.

Bring it Home

Suppose you found a species of animal that you had never seen before. How would you identify it? Scientists use a tool called a taxonomic key to determine an organism’s identity. A key uses a set of statements that describe an organism’s appearance to help identify the organism.

Most taxonomic keys are dichotomous, which means they offer only two choices for a specific feature. You select the most correct possibility and are directed to another statement. Eventually, you create a route through a series of statements that ends at the correct name of the unknown organism.

The best way to understand how a dichotomous key works is to try using one. The simplified key below can be used to distinguish between the most common insect orders. Use this tool to identify the insects shown below. As you can see, the identification is based upon the physical features of the insects. Choose one of the insects pictured below and work through the description sets provided to reach a positive identification.simple insect key

You may also wish to explained upon this activity with an introductory lesson on the scientific classification system.  To learn more about insects and to advance your skills with the binomial naming system, take a look at my Introductory Entomology Unit Study. It includes numerous hands-on activities, as well as a a more comprehensive dichotomous key to insects.

Science Milestones

Visit my Science Milestones page to learn more about scientists whose discoveries and advancements have made a significant difference in our lives or who have advanced our understanding of the world around us.

October 3, 20134

I started teaching a new class – live and in person for my local homeschool community.  I am very excited to teach formally again and this format promises to be both very rewarding and very challenging.  Rewarding because I get to share my passion for science with a great group of middle level students – such a fun age!  Challenging because as a homeschool mom, I do not have a class set of materials and equipment as I did in the public school and the kids vary in age and ability.

The course I have outlined for this first trimester focuses on life science.  We will be covering everything from scientific classification, cell structure, food chains and webs, and biomes.  There is so much to cover that another challenge will be simply deciding what to include.

levels of classification foldableScientific Classification

In our first session, I introduced the topic of scientific classification and how to use a dichotomous key.  Here is a simple video by Mark Drollinger explaining the six kingdom system:

▶ Six Kingdoms of Classification by Mark Drollinger

There are 3 Domains – Bacteria (prokaryotic micoroorganisms), Archaea (single-celled microorganisms), and Eukarya (organism whose cells contain a nucleus and other structures (organelles) enclosed within membranes).  Domains can be further divided into Kingdoms.

Currently, there are 6 Kingdoms – PlantsAnimalsFungiProtistsArchaea, and Bacteria.  Note that some resources show 5 Kingdoms (Plants, Animals, Fungi, Protists, and Monera) – grouping Archaea and Monera together.

Each of these kingdoms can be further divided into Phylum, Class, Order, Family, Genus, Species.  Some resources will show more specific levels including (but not limited to) superorders, subfamilies, tribes, etc.  For the purposes of this class, we will be using the levels shown here in bold and underlined.

If you have a BrainPop subscription, you may also wish to see the video on  Classification.

Dichotomous Keys

After a brief introduction and Power Point presentation on scientific classification (I could have been more concise than I was, actually), I introduced dichotomous keys.  Dichotomous keys are a tool that is used to identify organisms and that consist of the answers to a series of questions.

Here is another video by Drollinger that illustrates how these tools are used:

▶ Dichotomous Key by Mark Drollinger

Working in small groups, the kids each removed one of his/her shoes and placed it on the table.  They then carefully examined each shoe, noting its characteristics. They then brainstormed two categories into which each shoe either fit or did not fit; thereafter physically dividing the shoes into the two categories.  They continued in this way until 

each shoe stood alone.  They then recorded their dichotomous key on butcher paper and shared it with the class.  One group (which ended up splintering into two due to creative differences) chose to take the assignment further and rather than create a key for shoes, made one for the popular game, Minecraft. As I’d anticipated, they weren’t as successful with this but I loved their passion and commitment to see it through.

As it was clear that some groups understood and some did not – I took them outside and began to walk them through identifying one of the trees nearby using a dichotomous key from a book I’d brought along, Trees to Know in Oregon by Edward Jensen.  Though I live now in California, this is one of the best field guides I have ever come across.  I highly recommend it to anyone in the Pacific Northwest.

For many of the kids, it was clear that they hadn’t had much experience looking at the characteristics of trees.  This real-time assessment provided me with a clear direction for our next session when we will be focusing upon plants.

scientific classificationFoldable

For homework, I asked the kids to create a flip book or foldable for their interactive science notebook.  We had a little trouble creating one from scratch in class that I did not anticipate.  I’ve thereby created one and provide it to you for your personal use – Levels of Classification. The photo collage at the top shows the sample I used in class. The graphic just above shows the foldable I created.  It is designed to open like a mini-book so you’ll want to download the PDF to get both pages.

  1. Print it out front/back
  2. Fold it in half hamburger style (the short, fat way)
  3. Cut along the black line between the classification levels on the front flap only
  4. Choose an animal (or plant) and write the name on front cover in upper left corner
  5. Research the taxonomy of your selected animal (or plant)
  6. Beneath the flap, write down the characteristics that are true of all those animals (or plants) at that classification level (the first level – Domain – is done for you). Feel free to draw little pictures to help you remember these characteristics.

I would love to see your kids’ work when they have finished.  Please post a link in the comments or feel free to email me a digital picture of their work.  If I get enough submissions, I’ll create a little slideshow. 🙂

July 18, 20104

We’ve been going to Indian Mary near Grants Pass every 4th of July holiday for nearly 15 years now. Each year, I spend a little time picking up the rocks along the shore and investigating the invertebrates that cling to the rocks. The past couple of years, since we are now “homeschoolers” we have gotten a little more scientific about our search and bring along tools for collecting. I hadn’t previously considered documenting our findings until this year.

rogue7Searching for aquatic critters is one of our favorite summer activities. The kids spent hours along the river rubbing the rocks to see what critters might fall off into the dish pan. We then carried this back to the campsite where we could sit in comfort of the shade to observe our specimens more closely.

In past years, I’ve always seen a number of dragonfly, mayfly and stonefly nymphs. Planaria worms have also been prevalent.  This year however, I didn’t find a single planaria and instead found numerous midge larva and leaches!  Quite a surprise.

Additionally, we discovered many translucent little gel-like bubbles attached to the rocks as well as a couple of white tissue-like cocoon shapes (shown below).  I am not certain what these are, however.

We pack along a few reference materials with which to identify our discoveries and to learn more about each specimen. Click on this link, A Guide to Aquatic Insects, for a free excerpt from Science Logic: Ecology Explorations.  Using these references, the kiddos and I spend some time sketching and taking notes in our nature journals.

As I shared our discoveries with friends and family with whom we were camping, it was brought to my attention that a notice had been posted near the restrooms that a health concern regarding the portability of the water had been issued due to the water turbidity.  Turbidity is the cloudiness of a liquid caused by individual particles or suspended solids that are generally invisible to the naked eye, similar to smoke in. The measurement of turbidity is a key test of water quality.

Using another key test of water quality, I was delighted that we had determined this for ourselves!