Plant

From the time of Aristotle until the 1950s, most people classified all organisms into the animal kingdom or the plant kingdom. Fungi and plant-like, single-celled organisms were placed into the plant kingdom, in view of certain highly derived, but superficial characteristics of these organisms.

In 1959, Robert Whittaker advocated a five-kingdom classification system. According to a recent modification of that system, the five kingdoms are: Monera (single-celled, prokaryotic organisms, such as bacteria), Protoctista (various eukaryotic groups, such as algae and water molds), Fungi (spore-forming eukaryotes which lack flagella, such as mushrooms and various molds), Animalia (various multicellular eukaryotic groups, such as jellyfish and vertebrates), and Plantae, or plants.

Biologists now recognize an additional kingdom of prokaryotes, the Archaebacteria or ancient bacteria, which have unique characteristics that distinguish them from Eubacteria, or true bacteria in the kingdom Monera. The evolutionary relationships of Eukaryotes, Archaebacteria, and Eubacteria are uncertain at the present time. Undoubtedly, as our knowledge of evolution and biological diversity increases, Whittaker's five kingdom classification system will require further modification.