1. How to Use a Dichotomous Key Field and Museum Skills; Series 8400 Program 8417 Written by Communication Skills Corporation Modified by UM-D SLC Staff May 2001

2. Prerequisites Do not proceed with this module unless you have mastered the following prerequisite skills: –Knowledge of the concept of taxonomic categories – Kingdom, phylum, class, order, family, genus, species, and general anatomy of vertebrates, invertebrates, and flowers.

3. Objectives To enable you to understand the concept of a dichotomous key by identifying: common desk items, animals to phylum and class, and flowering plants to family. The posttest will have you constructing a dichotomous key of your own to identify several items.

4. Supplies Make sure that the following items are present in the tray: staplereraser pencil wooden ruler penthumb tack scissorsrubber band thin nailpaper clip If any of these materials are missing, please inform the SLC staff before continuing. You should also have a study guide handout. If you are using this online, visit here to view the sheet.here

5. Using Couplets The key to common desk items is organized in couplets. Couplet 1 consists of two differentiating choices - a and b, and instructions for which couplet to go to next - 2 or 3. Couplet 2 is shown which consists of two choices and in this example also indicates the identity of items fitting the key at this point. #Choice-Description Response 1aMade of wood 2 1bNot made of wood 3 2aContains graphite pencil 2bDoes not contain graphite wooden ruler

6. Use the Key to Common Desk items provided in your study guide. Divide the items into two groups: 1aMade of wood 2 1bNot made of wood 3 Wooden ItemsNon-Wooden Items Common Desk Items

7. Divide the wooden items according to: 2aContains graphite pencil 2bDoes not contain graphite wooden ruler Only one items is in each category and you have thus identified these items. Set the pencil and ruler aside. Contains graphiteDoes not contain graphite

8. Having eliminated the wooden items, divide the rest of the desk items into two groups according to: 3aMade of rubber/rubber-like material 4 3bNot made rubber/rubber-like material 5 Rubber/rubber-likeNon rubber/rubber-like

9. Group 3a includes two items. Divide the rubber items into groups according to: The rubber band and eraser have been identified. 4aMade in a loop pattern rubber band 4bA solid object eraser Made in a loop pattern A solid object

10. Divide the remainder of the items into groups according to: 5aMade of a single piece of material 6 5bNot made of a single piece of material 8 Single pieceNot a single piece

11. Divide the items composed of a single piece of material according to: The paper clip is in a category by itself, and now has been identified. Set it aside. 6aOne end definitely sharper than the other 7 6bBoth ends of similar sharpness paper clip One end sharper than otherBoth ends similar

12. Divide the items in category 6a according to: 7aSmall head straight pin 7bLarge head thumbtack There is only one item in each subgroup of couplet 7, and the straight pin and thumbtack have been identified. Small headLarge head

13. Divide the remaining items according to: 8aA cutting instrument scissors 8bNot for cutting 9 One items fits category 8a. The pair of scissors have been identified. Cutting instrumentNot for cutting

14. Separate the 8b items according to: The ball point pen and the stapler now have been identified. A given key represents but one possible way to describe items. 9aContains ink ball-point pen 9bDoes not contain inkstapler Contains inkDoes not contain ink

15. For review, key out the pair of scissors as though it was unidentified. The trail is as follows: 1bNot made of wood 3 3bNot made rubber/rubber-like material 5 5bNot made of a single piece of material 8 8aA cutting instrument scissors Notice that the key becomes more specific as you proceed through it. Try keying out another desk item if you are still unsure of the technique. Keep a running list of the couplets you have chosen so that you and your instructor can check the work.

16. Dichotomous Keys

17. Using a Dichotomous Key Dichotomous: made of two parts Dichotomous keys present two options at each step The user chooses a path based on the characteristics of the object Eventually the user is led to the name of the object

18. Turn to the key of Major Animal Groups in your study guide and consider the illustrated organism. It has a vertebral column or backbone and thus fits category (1a), Phylum Chordata, which sends you to couplet 2. Major Animal Groups 1aVertebral column present Phylum Chordata 2 1bVertebral column absent8 Vertebral column (backbone)

19. It has no hair, which sends you to 3. You notice there are no feathers, you proceed to 4. 2aHair presentClass Mammalia 2bHair absent3 3aFeathers present Class Aves 3bFeathers absent4

20. It has fins, so you move to 5. There are jaws, go to 6. 4aFins present5 4bFins absent7 5aJaws present6 5bJaws absent Class Agnatha Jaws Fins

21. Its gills are covered by an operculum which places the organism in Class Osteichthyes, the true bony fish. 6aGills covered by an operculum Class Osteichthyes 6bGills not covered by an operculum Class Chondrichtyes Operculum

22. Consider another organism, one having no vertebrate column. Therefore it fits category b of couplet 1, sending you to 8. 1aVertebral column present Phylum Chordata 2 1bVertebral column absent8

23. The organism is not radially symmetrical, sending you to couplet 10. An exoskeleton is present, sending you to 11. 8aBody symmetry radial 9 8bBody symmetry not radial10 10aExoskeleton present11 10bExoskeleton absent12

24. It has jointed legs. It is in Phylum Arthropoda, go to couplet 13. The organism possesses fewer than 5 pairs of legs. Go to couplet 15. 11aJointed legs present Phylum Anthropoda 13 11bJointed legs absent Phylum Mollusca 13aWalking legs, more than 5 pair14 13bWalking legs, 5 or fewer pairs15

25. Antennae are present, go to couplet 16. The organism possesses one pair of antennae so it belongs to class Insecta. 15aAntennae present16 15bAntennae absent Class Arachnida 16aAntennae, 1 pair Class Insecta 16bAntennae, more than 1 pair Class Crustacea

26. Major Plant Families Sepal Turn to the key to Major Plant Families in your study guide.

27. The flower parts are in threes and the leaves are mostly parallel-veined. parallel-veined. Proceed to couplet 2. 1aFlower parts in 3’s or multiples of 2 three; leaves mostly parallel-veined 1bFlower parts in 4’s or 5’s or multiples 9 of these numbers; leaves mostly net-veined

28. ovary is above the outer circle of flower parts and is therefore superiorPetals are present There is only one pistil The ovary is above the outer circle of flower parts and is therefore superior. Go to couplet 5. Petals are present, go to couplet 6. There is only one pistil, go to couplet 8. 2aOvary inferior3 2bOvary superior5 5aPetals are absent; plants grasslike7 5bPetals present; plants usually 6 not grasslike 6a One pistil8 6bMore than one pistil Alismataceae Pistil

29. Sheaths are absent and the petals and sepals are the same color Liliaceae Sheaths are coverings that enclose the stem for some distance above the base of the connection of the leaf to the stem. Sheaths are absent and the petals and sepals are the same color. Thus the plan belongs to family Liliaceae. 8aLeaves without sheaths; petals and Liliaceae sepals similar in color 8bLeaves with sheaths; petals and sepals Commelinaceae unlike in color

30. Look at another plant specimen. The flower parts are in fives and the leaves are net-veined. The organism fits the category b of couplet 1. Proceed to couplet 9. 1aFlower parts in 3’s or multiples of 2 three; leaves mostly parallel-veined 1bFlower parts in 4’s or 5’s or multiples 9 of these numbers; leaves mostly net-veined

31. The ovary is superior which fits category (9a). Go to couplet 10. Only one pistil is present, go to couplet 12. 9aOvary superior10 9bOvary inferior17 10aMore than on pistil11 10bOne pistil12

32. Stipules are pairs of supplementary structures at the base of the leaf stalk or petioles. Stipules are present, proceed to couplet 15. 12aLeaves with stipules15 12bLeaves without stipules13

33. The flower is irregular, that is the petals are not all the same size and shape within the flower circle. Thus the plant is a member of the family Fabaceae. 15aFlowers regular16 15bFlowers irregular Fabaceae

34. This concludes this portion of this module. If you followed the procedures described, you will understand the concept of a dichotomous key because you identified common desk items, two animals to phylum or class and two flowering plants to family. To complete this module, you must obtain a posttest from the SLC staff, in which you will create your own dichotomous key using eight given items.