The Fungi, are well-known as mushrooms, toadstools, molds, and morels. Along with bacteria, fungi are the fundamental decomposers in nature, and the cause of many plant diseases, pneumonia, and ringworm. Humans use fungi for production of alcohol, cheese, penicillin, cyclosporin, as well as culinary delicacies. They are of great importance to plants because they form important symbiotic relationships with plant roots, called mycorrhizae.

They are organisms that may appear plant-like, but are more closely related to animals. They belong to a group called the opisthokonts, sharing similarities in how their sex cells are constructed. The body of a fungus has a mass of thread-like strands, called hyphae or mycelium. Some have an algae construction (thalloid). All fungi have chitin in their cells walls (similar to animals)