Many of the fungi are pathogens that infect plants and animals causing diseases of many kinds. The life cycles of many of these are complex and involve two or more host plants.
The rusts are specialized basidiomycetes that are parasites on plants. They have complex life cycles, and some produce five different kinds of spores in addition to basidiospores. Many rusts are heteroecious and complete their life cycles on two different kinds of host plants whereas autoecious parasites produce all of their different kinds of spores on a single host species. Well-known examples of heteroecious rusts are wheat rust, white pine blister rust, and cedar-apple rust.
Smuts are parasitic basidiomycetes that produce powdery masses of black spores enclosed in a membrane. This membrane is often found in the ovaries of species of grasses, or on their leaves. The smut life cycle is less complex than that of the rusts, and only one other kind of spore in addition to basidiospores is produced. All smuts complete their life cycle on only one kind of plant. Smuts live as saprobes in the soil, however, and readily attack developing seedlings planted in infected soil. Corn smut is common in the Midwest. Despite the unappetizing appearance of the spore masses and their dust-like texture, membrane-enclosed corn smut spore masses are considered delicacies in some cultures and are eaten either boiled or fried.