Fungus leaf symbioses Fungi can occur within leaves or stems as symptomless infections. These fungi are called endophytes. They live almost all their life cycle within the host, grow very slowly whilst the organ they colonize is alive, and do not cause any signs of infection. They may protect their host from animal grazing or other pathogenic fungal infection by the production of metabolites. However, these products can have dramatic effects on herbivorous animals, causing symptoms of fungal toxicosis similar to St. Anthony's Fire.
Some fungi can form slow-growing, very intimate associations with algal species.
These associations are called Lichens. They are adapted to occupy extreme or marginal environments, like bare rock faces, walls and house roofs. They are highly sensitive to pollution because they are under quite extreme environmental pressure, and their presence in an environment has become a useful indicator of a lack of urban and industrial pollution. Fungus insect symbioses Fungi can also associate with insect species. Some species of ants culture specific fungi on plant remains they bring to their nests.