What is the role of keys in taxonomy ? Illustrate with example

A key is a scheme for identificaion of animals and ji plants which is based on contrasting characters. Taxonomic keys are useful in identification of unknown organisms.
They are analytical in nature. They are of two types :
(a) Yoked or Indented key, (b) Bracketed key.
(a) Indented key: It gives sequence of choice between two or more characters of species. Correct choice is essential for identification. Take the example of family Ranuculaceae. Indented key is used to identify the genera in the family Ranunculaceae by considering the characters of the carpel and fruit of the specimens. The first choice begins with carpel with single ovule and achene type of fruit to contract to carpels being many ovuled and fruits are follicles.