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How to Make a Dichotomous Key

Last Updated: February 12, 2023 Fact Checked

This article was co-authored by Bess Ruff, MA . Bess Ruff is a Geography PhD student at Florida State University. She received her MA in Environmental Science and Management from the University of California, Santa Barbara in 2016. She has conducted survey work for marine spatial planning projects in the Caribbean and provided research support as a graduate fellow for the Sustainable Fisheries Group. This article has been fact-checked, ensuring the accuracy of any cited facts and confirming the authority of its sources. This article has been viewed 135,492 times.

A dichotomous key is a way of identifying specimens based on contrasting statements, usually about physical characteristics. [1] X Research source By drawing a series of contrasts, you are able to narrow down the specimen until you can correctly identify it. Dichotomous keys are often used in the sciences, such as biology and geology. To make your own dichotomous key, first, select the characteristics you can use to contrast your specimens, then formulate these as a series of statements or questions you can use to narrow them down.

Things You Should Know

• Create a list of characteristics for the specimens you're trying to identify. For example, you might list traits like black fur, striped fur, spotted fur, long tail, short tail, and so on. [2] X Research source
• Focus primarily on characteristics that can be used to differentiate the specimens. If one specimen has fur and another has feathers, those would be good characteristics to list.
• Use the listed characteristics to divide your specimens into groups, like specimens with feathers and specimens with scales.
• Start with two groups, then divide each of those into two groups, and so on until each specimen is differentiated from all of the other specimens.

Analyzing Your Specimens

• If you are trying to create a dichotomous key for a series of animals, you might see that some have feathers, some swim, some walk on legs, etc.
• For example, if you are trying to differentiate a set of big cats, you might note that some are brown, some are black, some have stripes, some have spots, some have long tails, some have short tails, and so on.

• However, a trait all of the animals share is not a good distinguishing factor. For example, since all big cats are warm-blooded, you wouldn't want to use that trait on your dichotomous key.

• When making your dichotomous key for big cats, you may find that some of the cats you are analyzing have dark fur, and some have light fur. You may also see that all of them have short hair. Finally, you see that some of them have long tails, but some of them have no tails at all.
• You would start your key with a question/statement about fur color. You wouldn’t need to ask a question about fur length, since all of the examples have short fur. You would follow up with a question about tail length, since tails are not common to all of the cats, and therefore are a less general characteristic.

Creating Your Key

• For example, "The cat has solid-colored fur” or “The cat has patterned fur” are statements that can be used to break specimens down into two groups.
• Include the question "Does the cat have solid-colored fur?” in your dichotomous key to divide the animals. If the answer is “Yes,” then the cat belongs in the solid-colored fur group. If the answer is “No,” then the cat belongs in the patterned-fur group.

• For example, separate your cats based on whether they have solid or patterned fur.
• Similarly, if you note that all of your specimens have either feathers or scales, then these could be your groups A and B. You can begin your key with the question “Does the animal have feathers?”

• For instance, you might notice that some of the animals in group A swim, and others don’t. This differentiation can form level C/D for group A.
• Likewise, you might see that some of the animals in group B have legs, and others don’t. This differentiation can form level C/D for group B.

• Some specimens will be differentiated before the end, as you work through your contrasting characteristics. For instance, you might find yourself looking at some birds, and some reptiles. You will break them down into these groups, then sub-divide the birds.
• Two of the birds swim, but one of them does not. The single land bird will be identified as such, but you will have to further differentiate the swimming birds.
• In this case, you notice that one of the swimming birds is ocean-going, and one is not. This characteristic can allow you to identify them more precisely (e.g., as a gull and a duck).

Completing Your Dichotomous Key

• You could also try organizing your key in the style of a flow chart. For instance, have a box that asks a question like “Does the cat have dark fur?” Then, have a “Yes” arrow leading one way, and a “No” arrow leading another way. The ends of the arrows can lead to new boxes where you ask the next questions.

• Q: ”Does the animal have feathers?” A: “No” (it has scales, so it is a reptile).
• Q: “Does the reptile have legs?” A: “No” (it is a snake, either a cobra or a python, given your specimens).
• Q: “Does the snake have a hood?” A: “No” (so it is not a cobra).
• Your specimen is identified as a python.

• For instance, "Does the cat have solid-colored fur or stripes?” is not a useful question for a dichotomous key. This question might differentiate solid-colored and striped cats from cats with spotted fur. However, since solid-colored and striped fur are themselves very different, this is not a useful category to work with.
• Instead, you might first have a question that asks about solid-colored vs. patterned fur, then follow up with another level of questions like “Does the cat have black fur?” and “Does the cat have stripes?”

Community Q&A

You Might Also Like

• ↑ https://ib.bioninja.com.au/standard-level/topic-5-evolution-and-biodi/53-classification-of-biodiv/dichotomous-keys.html
• ↑ https://www.amnh.org/content/download/1778/24821/file/hob_dichotomous.pdf
• ↑ https://www.youtube.com/watch?v=9943bdL91nY
• ↑ https://bio.libretexts.org/Bookshelves/Botany/Red_Seal_Landscape_Horticulturist_Identify_Plants_and_Plant_Requirements_I_(Nakano)/01%3A_Plant_Identification/1.11%3A_Introduction_to_Dichotomous_Keys
• ↑ https://creately.com/guides/what-is-a-dichotomous-key/

About This Article

To make a dichotomous key, start by making 2 groups, for example big cats with spots versus big cats without spots. Then, subdivide each of these groups into 2 more groups, like big cats with short tails, big cats with long tails, and big cats with no tails. Continue subdividing your groups until you can’t break them down anymore. Once your key is complete, draw it out as a “tree diagram,” in which each subdivided category forms another branch of the tree. Or, organize your findings into a flow chart. To learn how to test out your dichotomous key, keep reading! Did this summary help you? Yes No

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Rate the lesson plan, lesson plan, using dichotomous keys.

A dichotomous key is an important scientific tool, used to identify different organisms, based the organism’s observable traits. Dichotomous keys consist of a series of statements with two choices in each step that will lead users to the correct identification.

Scientists have catalogued 1.5 million species on Earth and estimate that there might be as many as 100 million more unidentified species (Giller, 2014). Classification keys are tools that provide a means to correctly identify different organisms, based on observable traits. Most such keys are created in a dichotomous format. Dichotomous literally means dividing into two parts (Merriam-Webster, 2014). A dichotomous key provides users with a series of statements with two choices that will eventually lead to the correct identification of the organism. To use a dichotomous key, one must be able to make accurate observations and follow directions carefully. Focus Questions: How can you identify an unknown organism? What types of characteristics can be used to identify an organism? How do you use a dichotomous key and why is a dichotomous key important?

Learning Target: I can construct and use a dichotomous key based on different organisms’ characteristics.

Preparation

(10-15 minutes) The instructor will find ten pictures of different plants and animals that depict the complete body of the organism rather than a partial or face shot. Pictures can be projected on a smart board or overhead projector, or magnets can be placed on the back of pictures for placement on the blackboard. Pictures should be diverse and have evident easily seen characteristics. The instructor will ask the students to observe traits of the displayed organisms. Dichotomous keys are based on observations, so the instructor should encourage students to use observable characteristics, rather than behaviors. For example, if the picture depicts an owl, accept the observation “they have eyes that face toward the front.” Do not accept the observation “they hunt at night.”

For the students’ dichotomous keys to work, the observations must be ones that the students can see in the pictures because not all students are at the same level of knowledge. Students will then use the pictures to model the process of creating a dichotomous key.

Download Attachment 1

Download Worksheet 1

Download Lesson Plan

Lesson Hook/Preview

A dichotomous key is an important scientific tool, used to identify different organisms, based the organism’s observable traits. Dichotomous keys consist of a series of statements with two choices in each step that will lead users to the correct identification. This type of key is not hard to use, but makes more sense when students undertake the process of making one before using it. The instructor will model the process before students begin work on their own keys. After the demonstration, students will first make a Branching Key using a picture of an organism of their choice. Once the Branching Key is completed, students will convert it into a written dichotomous key. The end product will be a poster displaying the student pictures, along with their written dichotomous keys.

(25-30 minutes)

3. After modeling the process, direct students to take out the ten pictures that they collected for their project. Students will then go through the same process to create a dichotomous key unique to their pictures.

4. Have students check another student’s key to make sure they “work” and are correct before working on their final presentation.

dichotomous key, organism

Assessment Materials

(15-20 minutes)

Students will make a poster with a written dichotomous key and pictures on the front and their branching keys (rough draft) on the back. Give each student a copy of the Worksheet 1, “Classification 1: Using Dichotomous Keys” for a grading rubric to guide them on the requirements for their project. After grading, students should display their dichotomous keys around the room for all students to observe.

(up to 1 hour)

Students will be given different unknown organisms with keys for identification and will work through the identification process. Sources of keys: internet or textbooks.

Instructors may also wish to use field guides for local areas, using pictures of animals or plants that students might see in their backyards or parks. Good sources are the Peterson First Guides. Also, the internet can be searched for “sample dichotomous keys” and will yield multiple examples.

Additional Resources

"Dichotomous." Merriam-Webster . Merriam-Webster, n.d. Web. 16 Aug. 2014.

< http://www.merriam-webster.com/dictionary/dichotomous. >

Giller, Geoffrey. "Are We Any Closer to Knowing How Many Species There Are on Earth?" Scientific American Global RSS . Scientific American, 8 Apr. 2014. Web. 16 Aug. 2014. < http://www.scientificamerican.com/article/are-we-any-closer-to-knowing-how- many-species-there-are-on-earth.>

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Lesson Plans

Last updated: January 9, 2018

Sockmonkey Science

Resources for Elementary and Middle School Science Teachers in Texas and Beyond

Dichotomous Key Worksheets and Activities

Teaching dichotomous keys to students can be a dry topic but it doesn’t have to be! You may not have noticed this about me…but I love science AND art. I try to find cross curricular opportunities when possible with ALL other subjects. But by far, my favorite combination is Science + Art as I find it to be a refreshing fusion. Anyone can pull off Science + Math, but building content rich dichotomous key activities fused with trees, fish and art? That takes real finesse. Not to toot my own horn or anything (toot, toot).

What IS a dichotomous key?

A dichotomous key is a system used by scientists to identify different parts of the natural world. They can be used to identify rocks, plants, trees, birds, reptiles and mammals.

Dichotomous keys are set up in a two question format, leading users through a set of choices designed to help them correctly identify the object of their inquisition. It sounds confusing, but it really isn’t once you get the hang of it.

Start with something familiar.

Depending on the skill level of your students, you may need to practice working through keys using a small sample of familiar objects with easily identifiable differences. I recommend using something like pasta, buttons or feathers as a starting point, but honestly, just about anything will do.

Sample Lab: Gather up 4-6 different types of uncooked pasta. Assign each pasta sample a letter (i.e. Sample A, B, C, D, E). Create a dichotomous key based on the pasta you have and let students identify the pasta types using the key.

Example key using macaroni, penne, farfalle, spaghetti and fettuccini.

1a: Pasta is hollow………………………………….Go to #2

1b: Pasta is solid……………………………………..Go to #3

2a: Pasta is smooth and curved……………..Macaroni

2b: Pasta is long and straight………………….Penne

3a: Pasta is shaped like a bow-tie…………..Farfalle

3b: Pasta is long and straight………………….Go to #4

4a: Pasta is round and thin……………………..Spaghetti

4b: Pasta is flat………………………………………..Fettuccini

Bookish Ways has an EXCELLENT starter pack of free, simple dichotomous key activity worksheets to help guide students if you don’t have the time to come up with your own.

If this is your student’s first exposure to a dichotomous key, ease them into it with a review of animal adaptations . This will familiarize them with the attention to detail required to work through and identify organisms, and eventually create a successful dichotomous key on their own.

Most dichotomous keys focus on one specific trait to lead the user to an answer, like leaf patterns on stems or fin shape of fish species. The example above chooses beak shape to help identify the mystery bird samples.

Make it interesting.

Once you feel your students have mastered the concept of the dichotomous key, the real fun can begin. Adding a narrative like a fishing trip to their identification and key creation process can make a world of difference in their enthusiasm (and retention). Capping off the unit with a fun art activity will make it even more memorable.

I built four unique sets of dichotomous key activities for my students based on evergreen trees and freshwater fish , and I must admit the students were much more enthusiastic about the “Fish Frenzy” set with the exquisite corpse art activity.

NEXT:  Teaching taxonomy?  Make sure you read this!

Don’t forget to follow me on  Facebook ,  Instagram ,  Pinterest  and  subscribe by email  to get a free pack of my  Science Borders.

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Published by Sockmonkey Science

My name is Mary and I am the mother of two amazing little boys. When I am not changing diapers, I teach elementary science. I have worked at a small charter school for the last five years and been fortunate to be part of a school that is supportive of science education. I will complete my M. Ed. later this year. View all posts by Sockmonkey Science

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Dichotomous Key: Comprehensive Guide With Editable Examples

In the field of biology, classification plays a major role. With new species being discovered every day, it’s important to have techniques in place to identify and classify them. One such tool is the dichotomous key. It helps identify organisms by directing the user to look at the known organisms.

In this simple guide, we will explain what is a dichotomous key and how to create one. Some examples are provided in the dichotomous key examples section; you can use any template to start your project right away. Download them as PNGs, JPEGs, SVGs or PDFs for publishing, printing, and sharing.

Dichotomous Key Definition

A dichotomous key is a tool used in biology and other scientific fields to help identify and classify organisms, objects, or other items based on their characteristics. Simply put, it is a method used to identify a species by answering a series of questions based on contrasting features (eg: physical characteristics) that have two possible outcomes.

“Dichotomous” means divided into two parts, hence the dichotomous keys always present two choices based on the key characteristics of the organism in each step. By correctly selecting the right choice at each stage, the user will be able to identify the name of the organism at the end. The further you divide the key, the more you learn about the specimen you are trying to identify.

Students and professionals use the dichotomous key to identify and classify objects (i.e. people, animals, plants, bacteria, etc.) into specific categories based on their characteristics. It’s the most commonly used form of classification or type of identification key used in biology as it simplifies identifying unknown organisms.

Simply put, it is a method used to identify a species by answering a series of questions based on contrasting features (eg: physical characteristics) that have two possible outcomes.

When creating a dichotomous key , both qualitative (i.e. physical attributes such as how the organism looks, what color it is, etc.) and quantitative (i.e. the number of legs, weight, height, etc.) factors are considered.

It can be done in both a graphical (as a branching flowchart or written format - series of paired statements organized sequentially).  Most often, they are used to identify plant and animal species, although it can be used to classify any object that can be identified by a set of observable characteristics.

To easily draw connections between species to better establish proposed phylogeny create Cladograms .

What is the dichotomous key used for

A dichotomous key is usually used for

• Identifying and categorizing organisms
• Helping students easily understand harder scientific concepts
• Organizing large amounts of information to make identification of an organism much easier

How to Make a Dichotomous Key  

Below we have listed the steps you need to follow when creating a dichotomous key.

Step 1: List down the characteristics

Pay attention to the specimens you are trying to identify with your dichotomous key. List down the characteristics that you can notice. For example, say you are trying to classify a group of animals. You may notice that some have feathers whereas others have legs, or some have long tails and others don’t.

Step 2: Organize the characteristics in order

When creating your dichotomous key, you need to start with the most general characteristics first, before moving to the more specific ones. So it helps to have identified the more obvious and less obvious contrasting characteristics among the specimen before creating your dichotomous key.

Step 3: Divide the specimens

You can use statements (i.e. has feathers and no feathers) or questions (does it have feathers?) to divide your specimens into two groups. The first differentiation should be made on the most general characteristic.

Step 4: Divide the specimen even further

Based on the next contrasting characteristic, divide the specimen further. For example, first, you may have grouped your animals as have feathers and have no feathers , in which case the ones with feathers can be categorized as birds while you can further subdivide the ones that have no feathers as having fur and having no fur . Continue to subdivide your specimen by asking enough questions until you have identified and named all of them.

Step 5:  Draw a dichotomous key diagram

You can either create a text-based dichotomous key or a graphical one where you can even use images of the specimen you are trying to identify. Here you can use a tree diagram or a flowchart as in the examples below.

Step 6: Test it out

Once you have completed your dichotomous key, test it out to see if it works. Focus on the specimen you are trying to identify and go through the questions in your dichotomous tree to see if you get it identified at the end. If you think the questions in your dichotomous key needs to be rearranged, make the necessary adjustments.

Best practices to keep in mind

• Consider only one characteristic at a time
• Use morphological or observable characteristics as much as you can
• Use major characteristics when dividing the organisms in the beginning and use lesser or less obvious characteristics to divide them into smaller groups
• When writing contrasting statements, rely on similar word formats (i.e. have feathers and don’t have feathers)
• Be specific in your statements and avoid repeating the same characteristics
• Use questions that lead to yes or no answers rather than statements

To draw connections between species to better establish evolutionary connections use a Phylogenetic Tree Maker

Dichotomous Key Examples

Let’s look at some examples to make more sense of what is a dichotomous key.

Dichotomous key for animals

Dichotomous key for insects

Dichotomous key for plants

Dichotomous key for leaves

Benefits of Dichotomous Key

Dichotomous keys offer several benefits in various scientific and educational contexts:

Accurate Identification: Dichotomous keys provide a systematic and accurate method for identifying organisms or objects by focusing on their key characteristics. This reduces the likelihood of misidentifications.

Easy to use: The keys are designed to be user-friendly, so they can be used by everyone from students to experts.

Consistency: Dichotomous keys follow a standardized format, using specific terminology and criteria, so that different users can consistently get to the same identification for the same item.

Great for learning: Dichotomous keys help students learn to observe, compare, and understand the characteristics of different organisms, so they can better understand the natural world.

Useful in research: In scientific research, these keys are useful for cataloging and documenting biodiversity, which is important for understanding species relationships and ecological dynamics. S

Helps with field work: Dichotomous keys are portable and can be used in the field, which makes them ideal for on-site surveys, ecological studies, and biodiversity assessments.

Any More Tips on Making a Dichotomous Key?

We hope that this guide will help you familiarize yourself with the dichotomous key method. Make use of the editable templates to get a headstart in class. Invite your friends/ students to edit them online, and make a fun group activity out of it.

Any more useful tips on creating a dichotomous key that our readers can rely on? Do share them in the comments section below.

FAQ About Dichotomous Keys

What are the different types of dichotomous keys.

Dichotomous keys are categorized into different types based on their form.

Nested style – This style of dichotomous keys shows the next identification question nested under its answer. Each question is indented, and as the dichotomous key grows, each question will be indented further from the one after to keep the chart organized.

Linked dichotomous key – This type of dichotomous key has questions written in a listed form, one after the other. Each answer on a row will lead to a question in a different line.

Branching tree – This is one of the most common types of dichotomous keys. It takes a tree diagram form where each question or characteristic of the organism forms a new branch of the tree.

How does a dichotomous key work/ how to use a dichotomous key?

A dichotomous key work by asking questions about an organism to which there is only a yes or no response. Depending on the yes or no answer, the researcher is taken on a certain path through levels of classification until the organism is identified. Before using the dichotomous key, the researcher should have some knowledge about the features of the type of organism being investigated.

What tools do you need to create a dichotomous key?

You can easily create a dichotomous key diagram on paper using a pen for drawing and pictures to paste on it for better classification. You can also use an online tool or software that will allow you to create the dichotomous key diagram online. This kind of tool comes with intuitive diagramming capabilities, features to add images, downloading the diagram in different image formats suitable for embedding and taking printouts, and also collaboration capabilities with which multiple people can work together on the same dichotomous key diagram.

Join over thousands of organizations that use Creately to brainstorm, plan, analyze, and execute their projects successfully.

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Amanda Athuraliya is the communication specialist/content writer at Creately, online diagramming and collaboration tool. She is an avid reader, a budding writer and a passionate researcher who loves to write about all kinds of topics.

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1.11: Introduction to Dichotomous Keys

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• Kwantlen Polytechnic University via KPU Zero Textbook Cost Program

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Learning Objectives

• Describe the characteristics of dichotomous keys.

A dichotomous key is a useful tool for the identification of things not known to the observer; for example, unfamiliar plant species. The typical dichotomous key, as shown in the example below, is made up of a series of descriptions, features or characteristics, arranged in pairs (couplets) of contrasting alternative choices (e.g., hairy vs. not hairy, bigger than a breadbox vs. not bigger than a breadbox, etc.). Each couplet is worked through sequentially until the correct determination is made.

Starting at the first couplet, choose which of the two alternatives best suits an object or thing, and proceed to the couplet number or answer indicated by that choice. The number of things being considered is reduced at each successive step in the key so that by a process of elimination the correct determination is made. A dichotomous key for plant identification is available online at this link to Oregon State University Dichotomous Key [New Tab] [1] .

Example Dichotomous Key

Example objects to identify: apple tree, water-lily, fir tree, dandelion, astroturf, seaweed .

1.a. found in water ………………………………………………………………………………………… go to 2

1.b. found on land ………………………………………………………………………………………….. go to 3

2.a. grows in salt water ………………………………………………………………………………….. seaweed

2.b. does not grow in salt water …………………………………………………………………….. water-lily

3.a. a real plant ………………………………………………………………………………………………. go to 4

3.b. not a real plant ……………………………………………………………………………………….. astroturf

4.a. grows more than 50 m tall ………………………………………………………………………. fir tree

4.b. grows less than 50 m tall ………………………………………………………………………… go to 5

5.a. produces yellow flowers …………………………………………………………………………. dandelion

5.b. does not produce yellow flowers ……………………………………………………………. apple tree

Or, the couplets may be grouped like this:

1.a. found in water ……………………………………………………………………………………………………….. 2

2.a. grows in salt water ……………………………………………………………………………………. seaweed

2.b. does not grow in salt water ……………………………………………………………………… water-lily

1.b. found on land ………………………………………………………………………………………………………… 3

3.a. real plant ……………………………………………………………………………………………………………….. 4

4.a. grows more than 50 m tall ……………………………………………………………………………. fir tree

4.b. grows less than 50 m tall ………………………………………………………………………………………. 5

5.b. does not produce yellow flowers ……………………………………………………………..apple tree

3.b. not a real plant …………………………………………………………………………………………. astroturf

Dichotomous keys may be simple or complex depending on what is being identified. For example, distinguishing obvious visible characteristics, such as structures for water movement in woody or herbaceous plant growth is straightforward. However, it should be noted that leaves, flowers, and fruit will not typically be available at the same time and return visits may be needed. Furthermore, differentiating minute plant parts such as reproductive structures requires the use of a hand lens or low magnification microscope for inspection and a thorough understanding of the descriptive terminology used in a dichotomous key.

• https://oregonstate.edu/trees/dichotomous_key.html ↵

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