Key is another taxonomical aid that helps in identification of plant and animal species. These keys are based on similarities and dissimilarities in characters, generally in a pair called couplet.

Each statement in a taxonomic key is referred to as a lead. For categorizing each taxonomic rank, such as family, genus, species, etc., different keys are used. It is also useful in identification of unknown organisms.

Keys are of two types- indented and bracketed keys. Indented key provides a sequence of choices between two or more statements while in bracketed key, a pair of contrasting characters are used.

(i) Indented key to identify different species of Rhododendron.

1. Leaves evergreen

2. leaves densely hairy below, orange or white hair; flower appears to have separate petals

………………………. Rhododendron groenlandicum

2. hair absent on leaves, flower has five petals fused in a shallow tube

………………………. Rhododendron maximus

1. Leaves deciduous

3. pink flowers with two free petals and three fused petals

………………………. Rhododendron canadense

3. white to pink flowers with all petals fused together

(ii) Bracketed key to identify different species of Rhododendron.

Leaves evergreen-----------------------------------------------2

1. Leaves deciduous-----------------------------------------------3

2. Leaves densely hairy below, orange or white hair; flower

appears to have separate petals

……….………………………. Rhododendron groenlandicum

2. Hair absent on leaves, flower has five petals fused in shallow

tube

………………………………..Rhododendron maximus

3. Pink flowers with two free petals and three fused petals

……………………………… Rhododendron canadense

3. White to pink flowers with all petals fused together-----4