Page 96 - Biology_F5

Principles of classification

Indented dichotomous key
In indented dichotomous key, pairs of contrasting statements are successively indented,
with equal distance from the left. Each statement (or lead) starts with the same character
being described, and they both begin with the same noun, such as leaves, corolla, and
petiole.
FOR ONLINE READING ONLY
Example: Indented dichotomous key for five plant species
1a. Flowers present

2a. Leaves small Abelia grandiflora
2b. Leaves large
3a. Flowers red, petals free Hibiscus rosa-sinensis

3b. Flowers red, petals connate into tube Delonix regia
1b. Flowers absent
4a. Tree with needle-like leaves Pinus sylvestris
4b. Shrub with leafy fronds Dryopteris filix-mas

Bracketed dichotomous keys
In bracketed dichotomous keys, sets of couplets are kept together (bracketed), and they
start at the same level near the margin. The couplets must be assigned with numbers
or letters. The user is provided with a pair of lead for identification of unidentified
organism or taxon and is directed by numbers to a subsequent lead, if the selected lead
does not provide the name.

Example 1: Bracketed dichotomous keys for five plant species

1a. Flowers present ..................................................2

1b. Flowers absent ...................................................3
2a. Leaves small .......................................................Abelia grandiflora

2b. Leaves large .......................................................4
3a. Tree with needle-like leaves ...............................Pinus sylvestris

3b. Shrub with leafy fronds ......................................Dryopteris filix-mas
4a. Flowers red, petals free ......................................Hibiscus rosa-sinensis
4b. Flowers red, petals connate into tube .................Delonix regia

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