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Trees and Keys (PCEC)

TopicBotany - Trees (Native)
Laboratory and Hands-on Activities - Collection / Sampling
Outdoor Skills - Identification
Outdoor Skills - Reading the Woods
Summary
Participants will construct an identification key to learn about sorting and classifying trees and their leaves.
Grade Level8 and up
Recommended SettingOutdoor
LocationPotlatch Conservation Education Center at Cook’s Lake, Casscoe
Contact
Education Program Coordinator, 870-241-3373
DurationOne to two hours
Suggested Number of Participants20 - 25
Special Conditions
One adult supervisor per 10 students; outdoor activities, weather permitting.
Objectives
  • Become familiar with leaf and twig structures.
  • Sort and classify leaves according to their characteristics.
  • Build an identification key for a set of leaves.
Key Terms*

Bud

Compound leaf

Deciduous tree

Dichotomous key

Evergreen tree

Leaflet

Palmate venation

Petiole

Pinnate venation

Simple leaf

Sinuses (leaf)

Terminal bud

Materials

Leaf maps
Two deciduous leaf sets of 5 - 10 leaves with the following criteria:

  • Each pressed and mounted or laminated
  • Each leaf being from a different tree species
  • Specimens should include a twig, at least two leaves and the terminal bud
  • One of the leaves should show its underside

Key leaves (mounted and labeled with the tree’s name)
Unknown leaves (same as the key leaves, except without names)
Books about trees or the forest habitat (see suggested reading)

Background

Classifying or sorting organisms into similar groups makes them easier to identify and study. Identification keys have been created to quickly sort and name an unknown organism. Participants should be familiar with the key terms mentioned above.

Procedure
  1. Hand out the leaf maps worksheet and ask participants to become familiar with leaves and twigs.
  2. Have participants spread the key leaves on a table or the floor and identify their traits using the leaf maps. They should make the following observations about each specimen, and add any traits important to leaf identification.
    • Is the leaf simple? (The blade will be in one piece with a bud at its base.) Or is it compound? (The blade is divided into leaflets that do not have a bud at the base. Instead there is one bud for the entire blade, made up of all the leaflets on a petiole.)
    • If the leaf is simple, what is the length and width of the blade?
    • If the leaf is compound, how many leaflets are there?
    • What shape is the blade (heart, oval, narrow)?
    • What colors are the leaf and the petiole?
    • Are the leaves and/or petiole hairy or fuzzy? If so, where (leaf top or bottom)?
    • Is the leaf venation (vein pattern)
      • Pinnate – feather-like with one main center vein having smaller secondary veins coming from it or
      • Palmate – all veins coming from a common origin like the fingers from the palm of the hand.
    • Does the blade have lobes and sinuses? If so, how many? Are they deep or shallow? What shape or pattern do they take (rounded or sharp, all alike or different)?
    • What kind of margin (edge) does the leaf have? (entirely smooth, finely toothed, coarsely toothed, double toothed which means teeth with teeth)
    • Describe any fruit or seeds (acorn, cone, pod).
  3. When the participants are feeling comfortable with the trait list, construct a flow chart of characteristics that will help divide the leaves into smaller and smaller groups.
  4. Look over the key leaves and choose two contrasting traits, one that fits about half the leaves and another that fits the other half. Separate the leaves into two groups based on the chosen characteristics. 
  5. For example, the entire key group could be divided into:
    • leaf simple 
    • leaf compound
  6. Repeat for each of the groups. Continue until only one leaf in each group remains.
  7. After the flow chart is complete, use it to construct a dichotomous identification key. Dichotomous means two branches, referring to the two contrasting traits observed in each step of the identification process. For example:
    • 1a leaf simple; go to 2
    • 1b leaf compound; go to black hickory
  8. Set the key leaves aside and take out the unknown leaves. Test the key by using it to identify the unknowns. Check results by comparing the identification of the unknown leaves to the key leaves since they contain the same leaves. If any trees were identified incorrectly, something is probably wrong with the key. Correct the problem.
  9. For a final test, trade the constructed key and unknown leaves with another group. Each group should test the other group’s key and write a critique.
  10. Use a classification key that includes deciduous trees and evergreen trees to identify trees in the participant’s neighborhood or schoolyard.
Modifications

Supply a list of “required” leaves for participants to collect, identify and press for a collection.

Review
  • What is the difference between a simple and compound leaf?
  • How do deciduous and evergreen trees differ? Name some of each found in the area.
  • What is venation? Give examples of the different types of venation.
Resources
  • Wirth, Victoria (1991), Whisper from the Woods, Green Tiger Press.
  • Cherry, Lynne (1990), The Great Kapok Tree, Harcourt Brace & Company.
  • McGee, Marni (1994), Forest Child, Aladdin Paperbacks.
  • Fulton, Bill and Liz (2000), Arkansas Trees, efulton@aristotle.net
  • Moore, Dwight, Trees of Arkansas, Arkansas Forestry Commission.
Related Documents
Glossary

Bud – undeveloped shoot that normally appears on a stem containing a leaf bud, flower bud or both (mixed bud)

Compound leaf – leaf that is divided into two or more distinct leaflets

Deciduous tree – tree that periodically loses all its leaves (in autumn); most North American broadleaf trees are deciduous as well as a few conifers, such as the larch and cypress

Dichotomous key – tool that helps identity items in nature such as trees, wildflowers, mammals, reptiles, rocks and fish through a series of choices that leads to the correct identification

Evergreen tree – tree that retains its leaves year-round, generally a conifer

Leaflet – one of the separate blades or divisions of a compound leaf

Palmate venation – veins radiating outward from the base of the leaf like fingers spread out from the palm of the hand

Petiole – slender stem that supports the blade of a leaf

Pinnate venation – vein arrangement with one main vein extending from the base to the tip of the leaf and smaller veins branching off the main vein

Simple leaf – leaf having one blade, or a lobed leaf in which the separate parts do not reach down to the midrib

Sinuses (leaf) – area between lobes. (maples and oaks are typical examples of trees with "lobes" and "sinuses".)

Terminal bud – located at the end of a twig, marking the end of that year's growth