But they actually take on a great diversity of forms. One important aspect of fungi is their interaction with other organisims. Many are parasitic. Fungi are responsible for several major plant diseases. But others are symbiotic.
Lichens are a symbiotic relationship between a fungus and a green alga or cyanobacterium .
The very small, fine fungal hyphae are able to absorb minerals in the soil much more efficiently the plant's roots. The plant makes use of the minerals accumulated by the fungus. In exchange, the fungus gets its energy by absorbing carbohydrates that the plant makes via photosynthesis. About four-fifths of vascular plants form mycorrhizae, and many plants cannot survive without their fungal partners. General Fungus Information Introduction to Fungi Part of the Berkely Phylogeny of Life site.