Evolution of multicellular eukaryotes increased the size and complexity of organisms, allowing them to exploit the terrestrial habitat. Fungi first evolved in water but made the transition to land through the development of specialized structures that prevented their drying out. First classified as plants , fungi are now considered different enough from plants to be placed in a separate kingdom. Body Plans and Nutritional Modes Fungi contain unicellular, multinucleate, and multicellular forms. They are classified on the basis of their reproductive spores and the nature of their multinucleate or multicellular filaments known as hyphae .
Fungal cells have cell walls containing the carbohydrate chitin .
Fungal hyphae have a small volume but large surface area, enhancing the fungal absorptive capacity. Fungal hyphae are collectively termed a mycelium . Some fungi are saprophytes , they obtain their food from the decaying bodies of plants and animals. Other fungi are parasites . Fungi are important both as a source of food and in the preparation of food.