The two-kingdom classification system was given by Linnaeus in 1758. He classified all the known living beings into two categories- Animalia and Plantae on the basis of presence or absence of cell wall in their cells. As bacteria, algae, blue green algae, fungi, mosses, ferns, gymnosperms and angiosperms have the cells surrounded by cell walls, unlike animals, therefore, they were placed together under kingdom Plantae.