Scientific Name: Triglochin maritima and T. palustris
Distribution: Northern and Western United States and Canada
Type of Poison: Hydrocyanic acid or prussic acid
Signs of Poisoning:
Growth Characteristics: Arrowgrass is a wandlike herbaceous, obligate, wetland plant 12 to 40 inches tall with rhizomes. Stems are closely tufted on a proliferating rhizome. Reproduction is from rhizomes and seed. Growth starts in early spring and flowering occurs June to August.
Seedhead: Rather inconspicuous flowers on several to many short, green pedicels spaced along a spikelike raceme. Fruits are almost cylindrical, up to 1/4 inch long, and fall from the plant at maturity.
Leaves: Leaves are linear, 3 to 8 inches long, narrow and flattened or channeled. Short (less than 1/4 inch), membranous, entire or slightly bilobed ligules are present at the sheathing base.
Arrowgrass is widely distributed throughout the northern and western United States. It grows on wet, alkaline soils and may be found growing over large areas or small patches near springs. Arrowgrass starts growing in early spring. It is often found growing in native meadows that are cut for hay.
Arrowgrass that has adequate moisture does not cause poisoning. When growth is stunted from lack of moisture or frost, plants quickly become toxic.
The amount of arrowgrass required to poison sheep or cattle depends on the amount of poison in the plants and the rate at which the plants are eaten. About one-fiftieth of an ounce of hydrocyanic acid (one-fourth to 3 pounds of stunted arrowgrass) may kill a 600-pound animal. The toxic dose must be eaten in a single meal to cause death because the poison is not cumulative. Death results from respiratory failure.
L.F. James, R.F. Keeler, A.E. Johnson, M.C. Williams, E.H. Cronin, and J.D. Olsen. Plants Poisonous to Livestock in the Western States. U.S. Department of Agriculture, Agriculture Information Bulletin 415, 90 pp. 1980.
Pratt, Mindy S. Arrowgrass. Range Plants of Utah. 2008. Utah State University Extension Service. 29 June 2009. http://extension.usu.edu/rangeplants/htm/arrowgrass.