Identification Keys

Four ways to identify plants:

1. Expert determination - takes long time.
2. Recognition - based on past experience, not possible in some taxa, not practical if go to new area.
3. Comparison - with named specimens, photos, illustrations or descriptions. Very time consuming and not readily available for most plants.
4. Keys - most widely used method. Once you know the terminology you can identify a plant from anywhere.

Key - Artificial analytical device or arrangement whereby a choice is provided between two contradictory propositions resulting in the acceptance of one and the rejection of the other. First used by Lamarck in 1778.

• Couplet - a pair of contradictory propositions.
• Lead - each single statement of a couplet.
• Dichotomous - branched.

Two types of keys:

1. Indented or yoked - successive indentations. Advantage - groups similar elements. Disadvantage - wastes space.
2. Bracketed - two leads always together. Advantage - saves space. Disadvantage - similar elements far apart.

Construction of keys

1. Always dichotomous
2. Select characters in opposition to each other so leads are two contradictory propositions.
3. Only positive statements.
4. Initial word of each couplet should be identical.
5. Two consecutive couplets should not begin with same word.
6. No overlapping measurements or vague statements such as big, long or short.
7. Use macroscopic features.
8. Account for dioecious plants, i.e. both sexes.
9. Mention name of parts first e.g. leaves alternate vs. alternate leaves.
10. Use short statements.

Use of keys

1. Use appropriate key for region.
2. Read introductory comments on format, abbreviations, etc. first.
3. Read both couplets first before making a choice.
4. Use glossary.
5. Take several measurements rather than one observation.
6. Try both couplets when information is insufficient or unclear.
7. Verify results by reading description, comparing illustration or herbarium specimen.

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