Linnaeus' Work

In the 18th century, Swedish botanist Carolus Linnaeus developed the first effective classification system. He grouped organisms according to structural similarities. Those with exactly the same set of structural features were put in the same group. His classification system, with the same modifications, is what is being used today.

Linnaeus divided plants into classes according to the flower's number of stamens which he called the male elements. The classes were further subdivided into smaller groups called orders. Orders were grouped based on the flower's number of pistil or female elements. He subdivided the orders further into groups of organisms with minor differences. He called the subdivision genus (pl. genera) which was further subdivided into species (see Table).

Table Linnaues' Classification of plants. This table shos how the plant Euphorbia opio is classified.

Class	DODECANDRIA (12 stamens)
Order	Trigynia (3 pistil)
Genus	Euphorbia, genus of the spurges (plants with milky juice and flowers without petals and sepals (like poinsettia)
Species	apios, a spurge found on steep hills

Linnaeus also classified animals into six groups called classes. These are: 1.) quadrupeds; 2) birds; 3)reptiles; 4) fish; 5) insects; and 6) worms.
Animals with unusual forms like clams and earthworms, were included in the class of worms.