More than 1000 species of Ustilaginales live parasitically on hosts of more than 75 angiosperm families. They produce dark, powder-like traces consisting of fruiting bodies strung together on leaves, shoots, flowers, and fruits. They develop usually no haustoria. Their extensive mycelium spreads through the intercellular spaces of the host plants. Uredinales include about 4,000 species in 100 genera.
Smuts develop haustoria and infect a range of angiosperms, gymnosperms, and pteridophytes.
Puccinia graminis is the classic example of a fungus with an alteration of hosts. P. graminis is characterized by a complex alternation of generations. Up to five different types of spores can be generated during its course. P. graminis can live on grasses for an infinite time in its dicariontic state, if barberry is not present. Wind can on the other hand disperse fungus spores thousands of kilometres so that a local extermination of barberry provides no lasting protection against Puccinia .