Q.Define a taxon. Give some examples of taxa at different hierarchical levels.

A taxon is any unit or category used in the classification of living organisms — a rank in the taxonomic hierarchy that stands for a real group of organisms sharing common characters. Each rank, from species at the bottom up to kingdom at the top, is a taxon, and the whole set of ranks together forms the taxonomic hierarchy.

Examples of taxa at different levels:

• Species — the lowest taxon, e.g. sapiens in Homo sapiens, or the mango species Mangifera indica.
• Genus — a group of closely related species, e.g. Panthera (lion, tiger, leopard) or Solanum (potato, brinjal).
• Family — a group of related genera, e.g. Solanaceae (grouping Solanum, Petunia and Datura) or Felidae. …

When we look at the living world we cannot study each of its millions of organisms one by one, so biologists group them. Classification is the process of placing organisms into convenient categories on the basis of easily observed characters, and each such category is called a taxon (plural: taxa). Familiar words such as "dog", "mammal", "wheat" and "plant" each instantly bring to mind a set of features — every one of them is a taxon.

The important idea is that taxa exist at different levels. A dog is a mammal, and a mammal is an animal, so "dog", "mammal" and "animal" are all taxa, but they sit at successively higher levels. Sorting organisms into such taxa on the basis of their characteristics is called taxonomy, and because classification proceeds as a series of steps, each step or rank is a taxonomic category. All the categories taken together make up the taxonomic hierarchy.

The common set of categories, arranged from lowest to highest, gives us clear examples of taxa at different hierarchical levels:

• Species (lowest) — a group of individuals sharing fundamental similarities, distinguished from close relatives by morphological differences, e.g. sapiens in Homo sapiens.
• Genus — an aggregate of closely related species, e.g. Panthera, which includes the lion, tiger and leopard. …