Leaf Classification

INTRODUCTION

Trees are the largest kinds of plants and they all have three things in common. All trees have roots, a trunk and leaves. Leaves are very useful to the trees and they are also useful to us. With a Tree Finder field guide, trees can be identified by their leaves. This tree field guide is an example of a dichotomous key.

MATERIALS

• Tree Finder, Manual for the Identification of Trees by Their Leaves
• A wooded area to walk through or samples of a variety of leaves

WHAT TO DO

1. Look through the field guide to become familiar with it.
2. With partners or small groups walk through a wooded area and choose a tree to identify. Follow the directions in the Tree Finder to identify the chosen tree.
3. If a wooded area is not available, ask students to bring in samples of trees from their homes or neighborhoods. Pass these samples around to small groups in the class for identification using the field guide.

QUESTIONS

1. What is the first distinction made in the tree finder guide?
2. What steps would have led you to identifying a Trembling Aspen (Populus tremuloides)?

SUMMARY

Trees are classified into two main groups, angiosperms and gymnosperms. Angiosperms are classified into two groups as well, monocotyledon and dicotyledon. The dicotyledon group contains the broadleaf trees, such as the oak and maple and the monocotyledon group is made up of palms and lily trees. The word angiosperm refers to the fact that all species in the group are flowering plants that produce seeds enclosed by protective fruit. Gymnosperms do not produce flowers; instead, their seeds are exposed in cones and similar structures. The major types of trees in the gymnosperm group are conifers (needle-leaf trees such as the pine, spruce and fir), cycads and ginkgos.
With the help of a dichotomous key, one can classify and identify trees by looking at their silhouettes and leaves. A dichotomous key is a guide that presents questions with two possible answers in order to lead the user the identification information. For example, a dichotomous tree guide first asks if the tree has needles or leaves, then leads each answer in a different direction. It continues to ask questions and lead according to the answers, toward the final question that definitively identifies the tree in question. Each tree species has unique characteristics and the tree guide uses them to help users identify any tree.

SOURCES

"Tree," Microsoft Encarta Online Encyclopedia 2002.
http://encarta.msn.com
Leonard, Joan. Greenhouse Director, Department of Plant Biology, The Ohio State University.
Watts, May Theilgard. "Tree Finder," Nature Study Guild Publishers, Rochester, New York, 1991. ISBN 0-912550-01-5.

© S. Olesik, WOW Project, Ohio State University, 2003.