From Seed to Seed:
Plant Science for K-8 Educators

Activity 13: Leaf Peepers

Grades: 5-8

Associated Lesson Topics:

• Leaves
• Classification systems
• Role of leaves in photosynthesis

National Standards:

• SCIENCE: Standard C
• LANGUAGE ARTS: Reading 10

Planting the Seed...

Do all leaves look the same? Pass around some different types of leaves. What words would you use to describe these leaves? their edges? their surface? their vein patterns? their shape?

Teacher Information:

Although they seem quite simple, there are many ways to describe leaves. And an infinite number of different kinds of leaves exist in the natural world. In this activity, students will learn about the characteristics of leaves by looking at and comparing several different types. They will also learn how botanists, like Linnaeus, used these characteristics to classify plants by creating their own dichotomous key.

Dichotomous keys are keys that offer two-and only two-alternatives at each choice. Here are some rules for creating a dichotomous key:

1) The alternatives should be directly comparable, allowing for a single, clear choice to be made:

The second set of alternatives considers different characteristics. It is possible for a leaf to be hairy and serrated. Which characteristic would you pick?

2) When designing a key, subjective characters should be avoided:

3) The chosen characteristics should be consistent between individuals. If a sample leaf has a nick out of the corner, this should not be used as a characteristic. Students can determine the consistent characteristics by looking at more than one leaf.

4) The plant part in question should always be listed first:

While there are certain rules for making a dichotomous key, students still have quite a bit of freedom to be creative. However, at this level of detail it is possible for a set of alternatives to be accurate for two or more different species of leaves. Therefore, students need to double-check that individual keys in their guide do not allow for the improper identification of one another's leaves. Below is a sample dichotomous key to use for reference.

1. Leaves simple

2. Leaves smooth
3. Leaves alternate..........................................Oak

3. Leaves opposite..........................................Red maple

2. Leaves serrated.......................................................Birch

1. Leaves compound

4. Leaves three leaflets...............................................Common hoptree

4. Leaves five to seven leaflets..................................Ohio buckeye

Necessary Materials:

• Forest or nearby stand of trees.
• Leaf and tree guide.

*A note on field guides: Many field identification guides provide so much information that students easily become frustrated or are quickly misled. Be sure to choose an age-appropriate field guide. This is a difficult task. Below are a few suggestions for where to find field guides for different ages.

Procedure:

• Take a walk in the woods with your students and have each one pick a tree leaf that looks interesting to him or her. If you are unable to take a field trip, you can bring leaves into the classroom for students to use.
• Have each student develop a dichotomous key based on leaf characteristics. With your assistance, students can then use a published leaf and tree guide to identify what type of tree their leaves come from.
• Have the class compile its dichotomous keys into a local tree guide.
• Dry the tree leaves to include in the tree guide. You can do so by placing them between two pieces of newspaper under the weight of several heavy books. The leaves should be dry in about two weeks. Attach the leaves to large index cards using clear contact paper. Be sure to label the index cards with the name of the tree!

Harvesting the Crop...

Why do you think there are so many different kinds of leaves? How do you think the different features of leaves might help plants? What do you think the purpose of a leaf is? Could the differences among leaves help them to do their job more effectively? Compare leaves found locally to pictures of leaves in another ecosystem-a rainforest, for example-and question students about the differences they see. What do you notice when you compare the leaves from these two ecosystems? Why might leaves in the rainforest be so large?

Sources

• Leaf and tree guides
  Leaf & Tree Guide Rona Beame, Workman Publishing, 1989
  Carolina Biological Supply www.carolina.com
  
• Many cities have city tree guides that are free to schools and organizations.
  
  

  
  
  
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