The first modern dichotomous key was designed by Lamarck in his ‘Flore Francoise’ and he defined this as a way to reduce the time and effort required in plant identification. Taxonomic keys usually include characters that are relatively stable and easily observable. Single-access or sequential keys are always written in the form of dichotomous keys. The dichotomous keys are usually of two types: indented keys and bracketed keys. In bracketed keys, the contrasting characters in a couplet are placed together. Another type of identification device is the polyclave key. There are two types of multi access keys: edge punched cards and body punched cards. In edge punched cards, the sorting is done by means of elimination. In body punched cards, each card represents a particular character and the character states are marked in the form of numerous holes punched on the body of the card. The visual keys are based exclusively on images and minimal text.