1. U.S. Dep. Agric. 1970. Selected Weeds of the United States. Ag. Handbook No. 366. Washington, DC.
2. No. 20 of the series, “Intriguing World of Weeds.” Contributions are welcome and will be acknowledged. Send contributions to Larry W. Mitich.
3. Letters following this symbol are a WSSA-approved computer code from Composite List of Weeds, Weed Sci. 32, Suppl. 2. Available from WSSA, 309 West Clark Street, Champaign, IL 61820.