CLASSIFYING AND SEQUENCING: Part B

Constructing a Multi-Stage Classification Scheme

  1. A multi-stage classification scheme is also referred to as a dichotomous system. This means that each set is serially subdivided into two subsets until a subset contains only one kind of item. Such systems are often used to construct identifying keys to organisms.

    As in a binary scheme, subsets are determined by sorting objects that have a particular property from those that do not have that property. Animals, for example, may be classified as either having or not having a backbone. Those having a backbone may be further sorted into subsets that either have or do not have hair. Figure 2 shows a multi-stage classification scheme for the "creatures" from the first exercise.

    In addition to the characteristics already mentioned, a dichotomous classification system has the following features:
    1. Several other schemes may be possible, depending upon which observable properties are used for grouping.

    2. When each object in the original set is separated into a category by itself, the scheme is complete.

    3. A unique description of each object can be obtained by listing all the properties that the object has. In the above scheme, for example, creature 6 can be distinguished from the others in the original set by listing its properties: speckled body, not round, possessing a scalloped margin.


Figure 2. A multistage classification system.


  1. Now, it's your turn to make a multi-stage classification system. Cut out the "creatures" assembled below (Zogs, Thrakes, Blinches, etc.). On a separate sheet of paper, use these creatures to develop a "Multi-Stage Classification System." In each box, indicate the property such as color or shading, shape, etc. that you used to make the groupings. Be sure to carry the scheme through to completion (i.e., to the point where a given box contains only ONE KIND of "creature"). [Hint: Your system will be greatly simplified if you use multiple characteristics to establish subsets.]

  1. When your diagram is complete, make a list of all of the characteristics that together would be necessary to describe each kind of "creature" and differentiate it from the others:
    1. Zog --

    2. Thrake --

    3. Blinch --

    4. Dax --

    5. Storch --

  2. For additional practice, construct another dichotomous classification scheme for identifying all of students in your science class. Use a separate sheet for this exercise.

  3. A Dichotomous Key is a somewhat simplified version of the classification scheme boxes that you have been creating. Essentially, it is a series of paired statements that create the subsets. Each pair of statements is numbered, and the object fits into one of the categories described. That statement will then identify the object (if it is a single-member subset) OR it will send the reader to another numbered pair of statements for further defining. This continues until the reader of the key has arrived at the identity of a subset with a single member. We will use your first set of "creatures" to illustrate.

    1a. Body speckled (2)
    1b. Body not speckled (4)

    2a. Body round Rotunda
    2b. Body not round (3)

    3a. Body with scalloped margin: Floribunda
    3b. Body without scalloped margin: Digitorum

    4a. Body striped Alternata
    4b. Body not striped (5)

    5a. Rounded patterns on body: Ovalis
    5b. Body without circles: Amorpha

    Note that there is one set of paired statements less than the number of different kinds of items. This is fewest number of steps possible.

  4. Again, it's your turn. On a separate page, construct a dichotomous key to the second set of "creatures" assortment (i.e., thrakes, zogs, etc.). Use your multi-stage classification scheme (diagrammed in #2, above) as a guide. Remember that the number of steps should be one less than the number of different kinds of items.

  5. For additional practice, construct a dichotomous key for identifying all of students in your science class. Use a separate sheet of paper for this task.


A KEY TO THE COMMON EVERGREEN TREES IN THE FRONT RANGE OF THE ROCKY MOUNTAINSLove

1. Foliage leaves spirally arranged, needle-shaped, single or in bundles of 2 to 5; fruit a dry, scaly cone (2)
1. Foliage leaves scale-like, opposite, in pairs (12)

2. Leaves in bundles of 2 or more surrounded at base by a small sheath of thin scales; fruit a dry, woody cone (3)
2. Leaves single, without a sheath at base; scales of mature cones thin, leathery or papery (8)

3. Leaves 4 or 5 in a bundle (4)
3. Leaves 2 or 3 in a bundle (5)

4. Leaves 3.5-7.5 cm long, not sticky; cones large, 8-25 cm long, scales smooth, without spines; seeds not winged: Limber pine
4. Leaves 2.5-4.5 cm long, stick, stout and curved; cones 6-9 cm long, scales with spines (when young); seeds winged: Foxtail pine

5. Leaves short, 2-5 cm, generally in pairs; cones small, about equal length to that of needles, nearly spherical; seeds large, wingless, and edible: Pinon pine
5. Leaves 4-25 cm long, in bundles of 2 or 3. (6)

6. Leaves 4-7 cm (occasionally shorter), yellow-green; cones approx. same length as shorter leaves, persistent: Lodgepole pine
6. Leaves longer, 7-25 cm; cones 6-15 cm long (7)

7. Cones thick, hard; scales each with stout, hard prickle: Ponderosa pine
7. Cones yellowish-brown, shiny; scales usually with short prickle: Austrian pine

8. Leaves stiff, 4-angled, each jointed at base to small, hard, brownish, stem-like base; cones pendulous (9)
8. Leaves flat, not brown or wood at base; leaves fall entirely away, leaving scars on branches (10)

9. Leaves stiff, sharp-pointed; new twigs without hairs; cones more than 6 cm: Colorado blue spruce
9. Leaves less rigid and abruptly pointed; new twigs pubescent; cones less than 6 cm: Englemann spruce

10. Leaves narrowed toward base into short stalk that broadens slightly at the point of attachment; leaf scar elliptical; cones pendulous with 3-pointed bracts projecting: Douglas fir
10. Leaves not much narrowed at base; leaf scars large and circular; mature cone erect, dark purple or blackish, scales falling separately from axis of cone (11)

11. Leaves of lower branches 2.5-4.5 cm: Subalpine fir
11. Leaves of lower branches 4.5-7.5 cm; cones green, yellowish or purple: White fir

12. Fruit a berry-like structure, more or less juicy (13)
12. Fruit a cone about 1.2 cm, brownish-yellow; leaves scale-like, often glandular on back: Arbor vitae

13. Leaves awl-shaped, 6-15 mm; upper surfaces whitened; prostrate shrubs: Ground juniper
13. Leaves less than 6 mm; scale-like, not whitened above (14)

14. Leaves approx. 3 mm, pale to dark green, without hairs; fruit green, bluish-green to blue and also without hairs: Rocky Mountain juniper
14. Leaves less than 3 mm, dark green; fruit dark blue, without hairs at maturity (in Colorado, tree appears reddish-brown in winter: Eastern red cedar

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Notes on Evergreens of the Rocky Mountains:

Limber pines grow on wind-swept, rocky ridges, 8000 to 11,000 ft elevation.

Foxtail pines are uncommon, growing in very exposed positions up to 12,000 ft. elevation.

Lodgepole pines are found in nearly pure stands at 9,000 to 10,000 ft. elevation, usually where fire has swept through.

Ponderosa pine is the common pine of the foothills and the lower south-facing slopes.

Pinon pine is a small to medium-sized, much-branched and shrub-like tree of the southern mountains and also near Ft. Collins, Colorado.

The Colorado blue spruce is the state tree and grows singly or in groves in canyon bottoms and along streams in the foothills and montane zones.

Englemann spruce form extensive forests in the higher mountains from 8500 ft. to timberline.

Douglasfir is valuable for its strong durable wood. It forms large dense stands on north-facing slopes in the foothills and lower montane zone.

White firs occur with Englemann spruce at altitudes of 10,000 to 11,000 ft.

Introduction | Part A: Binary Systems| Part C: Sequencing

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