Ustilago is a genus in the smut fungi, which are the Ustilaginales. The smuts are major plant pathogens. There are no reports of human infection. No information is available regarding toxicity. Smuts have been documented as a cause of Type I allergies (hay fever, asthma). Ustilago is present in the air as dry brown spores (teliospores) and will grow in culture as a yeast (basidiospores). If viable Ustilago spores (dry, brown phase) are isolated on culturable (Andersen) sampling, the yeast phase will be the identifiable result. For more information please see "Smuts" in the primary spore list "Characteristics of Some Commonly Encountered Fungal Genera." Natural habitat includes grasses, cereal crops, weeds, other fungi, and other flowering plants (many types).