Lab 1: Vegetative Morphology & Keys

 

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Learning the vascular flora of Wisconsin requires familiarity with vegetative (sterile) and sexual (fertile) parts of plants — their morphology. This lab will be a review of vegetative features of plants with focus on flowering plants; vegetative aspects of ferns and their allies and the cone-bearing plants (gymnosperms) will be examined in the next lab.

Throughout the semester you will be using a variety of methods to identify and learn the vascular flora. The standard approach is with the aid of dichotomous keys, although computers have permitted additional polychotomous and expert identification methods. Using vegetative features of a number of plant species at two different scales — from a distance and close up — you will review the use and construction of dichotomous keys.

 

Vegetative morphology: (short review – see handouts). For a good review of descriptions and images of vegetative features, try the Plant Systematics website at Texas A&M.

I. Arrangement of leaves on stems - phyllotaxy

A. alternate
B. opposite
C. whorled

II. Leaf terminology

A. Parts

1. blade (= lamina)
2. petiole
3. stipules
4. node/internode
5. petiolate versus sessile

B. Compound versus simple leaf

1. simple leaf
2. compound leaf

a. pinnate
b. palmate
c. trifoliate
d. singly versus doubly

C. Venation

1. pinnate
2. palmate
3. parallel

D. Shape

1. filiform
2. awl-shaped
3 succulent

E. Margin

1. entire
2. toothed

F. Base (see handout)

1. peltate
2. truncate
3. cordate
4. decurrent
5. rounded

G. Apex (see handout)

H. Pubescence

1. glabrous
2. glaucous
3. tomentose

 

Morphology & Key exercise:

Fill in the “states” of each character of the four plants using the handouts. Construct a dichotomous key for the four genera using the above characteristics and the “construction of keys” handout as guides. You are constructing what is called an artificial key: it is not designed to reflect phylogenetic relationships, but rather to facilitate plant identification. Write two different keys for the plants, one focusing on basic leaf morphology and the other utilizing characters that are visible from 20 feet away. A good field key is often very different than a key that is well suited to herbarium specimens.

Feel free to work in groups of three or four on this exercise. The chart and the two keys should be handed in next lab period.

 

Asclepias	Nerium	Oxalis	Mimosa
				Phyllotaxy
				Compounding
				Leaf shape
				Lobing
				Leaf base
				Toothing
				Margin
				Pubescence
				Venation
				Armature
				Stipules

 

 

Dichtomous Keys:

1. The key should be strictly dichotomous throughout.

2. The statements in the two members of a pair (couplet) should be contrasting so that one fits the situation at hand while the other does not. For example:

a. Leaves opposite...................
a. Leaves alternate..................

3. The statements are usually in phrase form and are uniformly separated from one another by a semicolon. For example:

a. Leaves opposite; flowers blue; sepals 4.........
a. Leaves alternate; flowers red; sepals 5.........

4. To avoid unnecessary confusion the initial word of each lead of the couplet should be identical. Note that the first example is clearer than the second:

a. Flowers blue; sepals 5............
a. Flowers red; sepals 4.............

a. Flowers blue; sepals 5............
a. Corolla red; calyx of 4 sepals....

5. Also, for clarity, two consecutive couplets should not each commence with the same word. Note that the couplets of the first example are more sharply defined than those of the second:

a. Petals blue.......................
a. Petals red........................
b. Corolla actinomorphic.........
b. Corolla zygomorphic...........

a. Flowers blue......................
a. Flowers red.......................
b. Flowers actinomorphic.........
b. Flowers zygomorphic...........

6. Avoid the use of generalities or relative terms in contrasting leads of the couplet. Note how much more specific the first example is than the second:

a. Petioles 2-3 cm. long; flowers 5-8 cm. in diameter........
a. Petioles 6-7 cm. long; flowers 0.5-1 cm. in diameter......

a. Petioles short; flowers large and showy...................
a. Petioles long; flowers smaller and less conspicuous.......

7. Avoid using overlapping limits of variation. The following example is in poor form:

a. Petioles 2-6 cm. long; flowers pink to red......
a. Petioles 3-8 cm. long; flowers red to purple....

Here, petiole length and flower color should be avoided. Other, more contrasting, characters should be used in the key.