Abstract A description is provided for Ustilago longissima . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: Species of Glyceria , including G. maxima, G. fluitans, G. grandis, G. multiflora, G. nemoralis, G. obtusa, G. plicata, G. striata . DISEASE: Leaf stripe smut of Glyceria . Infected plants are slightly stunted, pale or yellowish-green, and usually fail to flower. Sporulation can occur throughout the growing season of the host. GEOGRAPHICAL DISTRIBUTION: Widespread, especially in north temperate regions. Asia: India (Nilgiri Hills), USSR (Siberia); Europe: Austria, Bulgaria, Czechoslovakia, Denmark, Finland, France, Germany, Hungary, Italy, Netherlands, Norway, Poland, Romania, Spain, Sweden, Switzerland, UK, USSR (Estonia, Republic of Georgia, Latvia, Russia), Yugoslavia; North America: Canada (Alberta, British Columbia, Man, NS, Ont, Que, Sask), USA (Connecticut, Colorado, Idaho, Illinois, Iowa, ME, Maine, Michigan, MN, MT, Nebraska, New Hampshire, New York, North Dakota, Oregon, Pennsylvania, Utah, Vermont, Washington State); South America: Argentina. TRANSMISSION: No detailed studies have been reported. The powdery ustilospores are readily disseminated by wind and water. Seed transmission is considered unlikely.