Plant diseases caused by fungi of the order *Uredinales
. Rust diseases are easily recognized by streaks of dark pustules on the leaves or stems. Autoecious rusts complete their life cycle on one host whereas heteroecious rusts have an alternate host for some of their spore stages. Many rust fungi cause economically important diseases. Rust of currant is caused by the heteroecious rust Cronartium ribicola whose alternate host is pine. Black stem rust of cereals (Puccinia graminis) has barberry (Berberis) as an alternate host.