How to construct Dichotomous key (classification ll ,High school Biology)

procedures considered when construction the key.

1.Morphological features should be used as much as possible
2.A single characteristic should be used at time
3.Major characteristics such as type of leaf and venation should be used first
4.paired statements that describe the variation in the characteristic should be stated eg .1(a) animal with legs
                   (b)animal without legs
5.Generalization and overlapping characteristics such as Height should be avoided UNLESS the height is categorized