- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6100) Unit Title: BOTANICAL CLASSIFICATION ____________________________________________________________________________ (CLF6103) Topic: USE OF THE PLANT Time Year(s) IDENTIFICATION KEY 1 hour 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (A-3) - Discuss three reasons for the current use of the modern system of plant classification (e.g., language barriers, universal names, and standardization of evolutionary similarities). (A-4) - List and discuss three applications the science of taxonomy has for the field of agriculture (e.g., plant, insect, and microorganism identification). Special Materials and Equipment: References: Bailey, L. H. (1976). HORTUS THIRD. New York: Macmillan. Harrington, H. D., & Durrell, L. W. (1957). HOW TO IDENTIFY PLANTS. Athens, OH: Ohio University Press. Hartmann, H. T., Flocker, W. J., & Kofranek, A. M. (1981). PLANT SCIENCE: GROWTH, DEVELOPMENT, AND UTILIZATION OF CULTIVATED PLANTS. Englewood Cliffs, NJ: Prentice-Hall. Evaluation: Instructor evaluation of plant identification activity. ===================================================================== *** INSTRUCTORS PLEASE NOTE *** The detail of this topic presentation goes beyond the scope necessary to meet the requirements of the Core Cluster in this area. It will take longer to teach than indicated above if covered entirely. It is included for local enrichment as appropriate to the class. ===================================================================== TOPIC PRESENTATION: USE OF THE PLANT IDENTIFICATION KEY INSTRUCTOR'S NOTE: This topic presentation should be made AFTER students have been familiarized with the terms dealing with the characteristics of leaves, fruits, and flowers (CLF6104, CLF6106, and CLF6107). A. Plant Identification Keys and Their Use: Plant identification keys (or "ID" keys, for short) are useful tools for determining a plant's identification by outlining and grouping related types. 1. Most keys we use will be limited in scope to the type of plants we are interested in. Examples are: a. Keys covering a particular plant family. a. Keys covering a group of plants which inhabit a certain geographical area. 2. A key which included, for instance, all flowering plants would be too cumbersome for use in most cases. 3. Ususally, a key is organized so that characteristics are compared in pairs. This simplifies the procedure of following the key through. Keying the plant becomes a series of yes-no decisions about plant characteristics offered in the key. Because there are only two choices regarding each characteristic, this kind of key is referred to as a dichotomous key. As a decison is made regarding each characteristic, the key either gives you the name of the plant, or gives you the next level of questions which must be answered to proceed with identification. 4. For keys that are designed for practical use in the field, the characteristics compared principally reflect morphological differences. More specialized keys, for use in the laboratory, may utilize more criteria based on physiology or evolutionary considerations. This also applies to keys for identifying other kinds of organisms such as bacteria, fungi, insects, and protazoans. B. Types of Keys: There are two basic kinds of keys in general use. 1. Bracket Key: The two choices stand together. The numbers are followed to find the next level of identifying characteristics. For example: 1. Plant has yellow flowers............................go to 2 1. Plant has red flowers...............................go to 5 2. Plant has simple leaves.........................go to 3 2. Plant has compound leaves.......................go to 4 3. Flower has 4 petals...............................Species A 3. Flower has 5 petals...............................Species B 4. Leaflets in Threes............................Species C 4. Leaflets 7 to 9...............................Species D 5. Flowers solitary..................................Species E 5. Flowers in clusters.................................go to 6 6. Inflorescence a spike.........................Species F 6. Inflorescence a panicle.......................Species G 2. Indented Key. This is more efficient to use, as indentations, rather than numbers, are used to indicate the subsequent levels of choices. 1. Plant has yellow flowers 2. Plant has simple leaves 3. Flower has 4 petals...................Species A 3. Flower has 5 petals...................Species B 2. Plant has compound leaves 4. Leaflets in Threes....................Species C 4. Leaflets 7 to 9.......................Species D 1. Plant has red flowers 5. Flowers solitary..............................Species E 5. Flowers in clusters 6. Inflorescence a spike.................Species F 6. Inflorescence a panicle...............Species G __________________________________________________________ ACTIVITY: 1. Using the sample keys below, have students identify the characteristics of each "species" of plant described. Working in groups, they will trace back the path taken to arrive at each species, and record the characteristics of each as they go. 2. Students will turn in to the instructor a list of all the "species" on their key, and a description of each. Half of the groups should use Key #1, the other half should use Key #2. 3. The class as a whole should discuss binomial plant names and common plant names for each of the theoretical "species," based on some distinguishing characteristic in the plant's description, or even the student(s) who first "identified" the "plant." EXAMPLE: Species "M" would be described as a plant with yellow flowers and compound leaves, with leaflets in threes and a glabrous surface on the leaflets. Students might give it the name "Trifolium aureum" or the golden three-leaf meadowflower. KEY #1 1. Plant has blue flowers.............................go to 2 1. Plant has orange flowers...........................go to 5 2. Plant has ovate leaves.........................go to 3 2. Plant has lanceolate leaves....................go to 4 3. Flower has petals in multiples of 2..............Species A 3. Flower has petals in multiples of 3..............Species B 4. Pinnate leaflets.............................Species C 4. Palmate leaflets.............................Species D 5. Flowers sessile..................................Species E 5. Flowers with pedicels..............................go to 6 6. Inflorescence a spike..........................go to 7 6. Inflorescence a panicle........................go to 8 7. Grows less than 2 feet tall......................Species F 7. Grows more than 3 feet tall......................Species G 8. Leaf margin serrate..........................Species H 8. Leaf margin dentate..........................Species I KEY #2. 1. Plant has yellow flowers 2. Plant has simple leaves 3. Flower has 4 petals...................Species J 3. Flower has 5 petals...................Species K 2. Plant has compound leaves 4. Leaflets in Threes 5. Leaflets pubescent............Species L 5. Leaflets glabrous.............Species M 4. Leaflets 7 to 9.......................Species N 1. Plant has red flowers 6. Flowers solitary..............................Species O 6. Flowers in clusters 7. Inflorescence an umbel................Species P 7. Inflorescence a compact head 8. Leaf apex acuminate...........Species Q 8. Leaf apex truncate............Species R __________________________________________________________ C. Common Difficulties in the Use of Plant ID Keys: While the examples above are straightforward and easy to follow, real plant keys are not easy to use for the beginner. Much practice is required, as is a broad knowlege of the many botanical terms encountered in the keys. Some of the things to watch for: 1. Very often, the key relies on characteristics that are not present on the sample you happen to have, i.e., the key gives the type of fruit or the development of the ovary, and the specimen you have available is only in the early stages of setting flower buds, and fruits won't be visible on the plant for two months. Often, a key relies on being able to view the structures associated with several stages of development. 2. Keys are designed for "normal" specimens. Often, the sample you have may be unusual in some way because of environmental conditions or even a genetic variation. 3. The exact meaning (or interpretation) of the terms used can vary somewhat according to the author of the manual (i.e., one botanist's "elliptic" is another's "oval," and so on). If you practice a lot with the same manual, you will become familiar with the nuances of each term. 4. The key may be incomplete, or in error. Like the people who make them, botanical keys are not perfect. Also, sheer logistics dictate that some omissions occur. For instance, if almost all of a particular genus have pink, white, or red flowers, and if there is one yellow exception, the yellow plant may be overlooked or left out in the interest of brevity. D. Recommendations for the Effective use of Plant ID Keys: 1. Inspect the whole plant before starting to key it out. Get the "big picture." 2. Check your progress at each step by reading the descriptions. For example, when you arrive at the genus in the key, read over the entire description of the genus. 3. If you can't decide which path to take, try both. Usually, it will become apparent before long which choice leads to a "dead end." 4. Related to this, always read both contrasting descriptions before deciding. The first one may sound so good that the second, and more correct, choice is overlooked. The contrast of the two categories will help explain each other. 4. Use your knowlege of the group to help, for instance, ruling a plant out of the monocots because, clearly, the seedling posesses two cotyledons. Think analytically. 5. Give more weight to the important characteristics in case of doubt. Usually floral and fruit structures have more importance than, for instance, the height a plant is said to grow. 6. Practice! E. Other Agricultural Applications of Identification Keys: Identification keys, such as the ones used by botanists and horticulturists, are used in many other diciplines relating to agriculture. The same taxonomic principles apply. The differences are only in the organisms and the terms associated with their particular morphological and physiological characteristics. Dichotomous keys can be used to identify many kinds of organisms, including: 1. Insects 2. Fungi 3. Bacteria 4. Mollusks 5. Nematodes 6. A wide variety of fish and mammals __________________________________________________________ ACTIVITY: 1. Obtain dichotomous keys for other disciplines, and have students identify some of the important kinds of characteristics used as criteria for the classification of those organisms, i.e., type of mouthparts and number of wings for insects as opposed to type of inflorescence and leaf arrangement for plants. __________________________________________________________ 1/7/91 MH/clh/dlc #%&C