Organisms are grouped (classified) by comparing structural (and more recently genetic) similarities, and using these to arrange species according to common ancestry. Several alternative classification schemes exist, based on different interpretations of these relationships; indeed classification systems are fairly frequently revised, particularly as a result of the extraordinary advances in molecular and DNA studies in recent years. One commonly used classification scheme is:
| Kingdom | Five kingdoms are usually recognised (Protoctista, Monera, Fungi, Plants, Animals) |
| Phylum | This is termed Division in the plant kingdom. |
| Class | |
| Order | |
| Family |
Highest group commonly used in Species classification (generally small enough to distinguish members). Family names for animals end in -idae, for plants in -aceae. |
| Genus | Highest group directly referred in scientific name. |
| Species | Epithet in scientific name. |
| Subspecies, Varieties, Forms, etc | All groups below Species will interbreed if isolating factors are removed. |
A number of further taxonomic sub-divisions (eg. superfamily, suborder, tribe) may be used to denote finer-scale groupings.
The Need for Classification Anonymous.
Taxonomy Wikipedia.