The plant kingdom. In most classifications this is taken to include all the green plants (i.e. all organisms containing chlorophyll). In many classifications the fungi and bacteria are also included. Plants are distinguished from members of the animal kingdom (Animalia) by a number of factors. Most are autotrophic, making their food from inorganic starting materials by photosynthesis. Animals by contrast are heterotrophic. However the fungi, most bacteria, and certain parasitic higher plants are also heterotrophic. Plants are usually attached to a substrate and not able to move around freely like animals (this however does not apply to certain flagellate algae and fungi). Plants can generally only respond to external stimuli by growth movements. Response is consequently very slow as compared to animal movements and only occurs if the stimulus is prolonged. Most plant cells are surrounded by cellulose cell walls and starch is a common storage polysaccharide. Animals do not have cellulose cell walls and carbohydrates are commonly stored as glycogen. Perennial plants tend to grow indefinitely while in animals increase in size usually ceases at maturity.
The Plantae has been variously divided into subkingdoms and divisions. Some systems recognize two subkingdoms, the Thallophyta and Embryophyta. See also algae, fungi, bacteria, Bryophyta, Tracheophyta.