The key for identification of plants is a taxonomic key. It is an important taxonomic aid. Key can be defined as a set of alternate characters arranged in such a manner that by selection and elimination one can quickly find out the name of an organism. Depending upon the category, a key may be class key, order key, family key, genus key and species key.
Taxonomic keys can be of two types
(i) Indented or Yolked key
(ii) Bracketed key
Indented key, provides a sequence of two or more alternate characters from which selection and elimination are carried out. In bracketed key, the alternate characters are given numbers in brackets. For example, take four genera of family-Ranunculaceae to explain this.
(i) Ranunculus Leaves alternate or radical, flowers not subtended by involucre, carpels ovuled, fruit achenes.
(ii) Clematis Leaves opposite, compound petals absent, sepals 4, carpels uniovulated and first achenes.
(iii) Nigella Flowers regular, carpels united at base, many ovulated, fruit follicles.
(iv) Anemone Leaves alternate or radical, flowers subtended by involucre, carpels 1-ovulated fruit achenes.