Triglochin maritima L., seaside arrowgrass, and T. palustris L., marsh arrowgrass, are widespread on wet saline and high lime soils in the Prairie Provinces of Canada. The morphology, ecology, and general biology of the two species are discussed with special emphasis on their poisonous properties. Triglochin is cyanogenic, and the hydrocyanic acid formed on injury to the plants sometimes causes severe cattle losses.