Dichotomous keys
A dichotomous plant key uses a
series of contrasting, paired
questions to identify a plant.
The key uses morphological
characteristics of the plant for
identification.
Dichotomous key decision tree structure
Paired question
Identified plant
Keys will be provided for the larger
genera studied in class such as the
oaks and maples.
The keys can help you identify the
different species in a genera as well
as help begin the process of problem
solving used to identify plants.
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Dichotomous keys
An example of a paired decision question might
involve leaf and bud characters. Given the sample
to the right, the key might look like this:
1. Leaf arrangement is alternate
2. Leaf margin is serrated
3. Buds are elongate, pointed ……… Fagus
3. Buds are obtuse
2. Leaf margin is entire ……… Cercis
1. Leaf arrangement is opposite
4. Leaf margin is entire
4. Leaf margin is serrated
Since the plant has an alternate leaf
arrangement, the first decision would be to
go to line 2 and make the next decision on
leaf margin. The leaf margin is serrated.
The next decision is on bud character until
Fagus becomes the appropriate choice.
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Dichotomous keys
Some keys do not number the
decisions and use only indentations.
This key might look like this:
Leaf arrangement is alternate
Leaf margin is serrated
Buds are elongate, pointed ……… Fagus
Buds are obtuse
Leaf margin is entire ……… Cercis
Leaf arrangement is opposite
Leaf margin is entire
Leaf margin is serrated
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Dichotomous keys
Dichotomous keys use morphological
characteristics as decision aids.
An abbreviated glossary of common
botanical and morphological terms can
be accessed the glossary terms link.
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