Endophytes are a type of symbiosis in which a fungus lives inside a vascular plant, generally in the leaf or stem. The
endophyte provides some benefits to the plant, but in the case of endophytes of ryegrass and tall fescue the endophyte also affects the health and reproduction of grazing animals that feed on the plant.
Endophyte hyphae run between the plant cells and are not visible to the naked eye. They produce no external
pustules, and there are no visual signs that the plant has the endophyte. The endophyte does not spread
between plants, but is present in the seed of infected plants. As result plants grown from that seed will be
infected with the endophyte.