Grade: 3 to 5 Length: one hour Subjects: life science, classification Topics: weed identification, dichotomous keys Objectives Exercises in this lesson help students achieve the following objectives: Practice observation skills, distinguish similar characteristics, and identify plants by using two simple dichotomous keys Create and use their own dichotomous keys Introduction Dichotomous keys are one of the tools available for weed identification. The use of keys encourages close examination of a subject and helps to sharpen observation and classification skills. Students will learn about dichotomous keys, apply this method for classification and identification to simple objects, and create their own keys. Before teaching this lesson, read the entire lesson, and make sure all materials are available. Background Dicho comes from the Greek word meaning in two or into two. When using a dichotomous key, you choose between two characteristics, follow the appropriate path, and go to another set of characteristics until the item you are examining is in a class by itself. At this end point, you find a scientific name for the item. Plants are often best known by their common names. However, common names are not universally accepted. Each geographical area tends to have its own common names for plants, and the results are often confusing. In the mid-eighteenth century, a Swedish botanist named Carolus Linnaeus developed the scientific naming system that is in use today. Names are based in Latin, and names may have Greek roots. The scientific name provides information on the genus and species of the life form. The first part of a scientific name is the genus. The genus is always capitalized, and it is usually assigned to a number of species with many characteristics in common. The second part of the scientific name describes the species. It is usually lower case, and it often describes a particular species with regard to color, size, or location in which it grows. Together, the two parts form the scientific name for the species. Scientific names, which are usually italicized in print, are used worldwide. Genus and species are the two final categories in a larger system of classification that includes the following categories: Kingdom Phylum Class Order Family Genus Species Invasives: Plants on the Move~~~~~~~~~~~~~~~~~ Weed Identification~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 117
Preparation Materials 1 five different kinds of small candies, such as dum-dums, Hershey kisses, smarties, starbursts, or jolly ranchers in approximately equal quantities Have available two pieces of candy for each student. Show students a bowl of candy, and ask students to identify the candy by its common name. 2 Explain that you have assigned a scientific name to each type of candy, and students may determine the scientific name only by using a key correctly. Students may keep the candy if they correctly identify the candy by its scientific name. Activity Materials 1 five different weed samples common to your area in approximately equal quantities Have two weeds available for each student. If live weed samples are unavailable, use three-dimensional models. copies of the Candy Key and Weed Key Template worksheets Have available one copy for each student. Complete the Weed Key Template with local plant species before making copies. Explain that a dichotomous key classifies objects based on similarities and differences. We rely on these similarities and differences to identify objects or organisms. Students will use dichotomous keys to help identify weeds growing in the community. 2 Explain that before using a dichotomous key to identify weeds, students will practice using a key to identify candy. Give a copy of the Candy Key to each student. Using a piece of candy, demonstrate how to use the key. 3 Pass around the bowl of candy. Ask each student to take two different kinds of candy. 4 Ask students to use the Candy Key to determine the scientific name you assigned to the different types of candy. Check students work for accuracy. 5 6 Give each student a copy of the Weed Key Template that you prepared in advance. Give each student two different weed specimens, and ask students to use the Weed Key Template to determine the scientific names of the weeds. Check students work for accuracy. Conclusion and Evaluation Conclude the lesson by reviewing the common and/or scientific names for the five weeds used in the Activity. Tell students where you collected the weeds. Discuss other locations where students have seen these weeds growing. Review some of the problems associated with invasive plants. Suggest that properly identifying plants is the first step in controlling invasive plants. To evaluate students, have students identify all five species of weeds used for the Activity. Independent Practice and Related Activities Ask students to develop their own dichotomous keys for other groups of objects or organisms. Have other students use the keys to test their accuracy. Take students into the field to practice identifying weeds in a field setting. Vocabulary classification, common name, dichotomous, identification, key, organism, scientific name Resources Peterson, Roger Tory and Margaret McKenny. A Field Guide to Wildflowers of Northeastern and Northcentral North America. Boston: Houghton Mifflin Company, 1968. 118 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Weed Identification ~~~~~~~~~~~~~~~ Invasives: Plants on the Move
Spellenberg, Richard. National Audubon Society Field Guide to North American Wildflowers, Western Region. 2nd ed. New York: Knopf, 2001. Weed identification guides from local extension offices or weed control departments of state and federal agencies. For three-dimensional models of weed specimens, contact the Center for Invasive Plant Management, 733 Leon Johnson Hall, MSU Bozeman, P.O. Box 173120, Bozeman, MT 59717-3120; 406-994-6832. cipm@montana.edu, www.weedcenter.org National Science Education Standards: As a result of their activities in grades 3 5, students should develop abilities in and an understanding of the following areas: Life Science Content Standard C: characteristics of organisms Invasives: Plants on the Move~~~~~~~~~~~~~~~~~ Weed Identification~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 119
120 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Weed Identification ~~~~~~~~~~~~~~~ Invasives: Plants on the Move
Invasives: Plants on the Move~~~~~~~~~~~~~~~~~ Weed Identification~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 121
Weedy Definitions classification placing plants and animals into groups, based on characteristics they have in common common name the name organisms are usually called; can vary from region to region dichotomous key method of classifying organisms by choosing between two characteristics identification something that proves what a plant or animal is During the lesson, you used a dichotomous key for plant identification. key a logical, orderly listing of characteristics used to identify organisms organism a living plant or animal scientific name the name an organism is given by the scientific community; made of two words, usually of Latin or Greek origin, the first of which lists the organism s genus and the second of which lists its species 122 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Weed Identification ~~~~~~~~~~~~~~~ Invasives: Plants on the Move