This section is from the book "A Guide To The Poisonous Plants And Weed Seeds Of Canada And The Northern United States", by Robert Boyd Thomson, H. B. Sifton. Also available from Amazon: A guide to the poisonous plants and weed seeds of Canada and the northern United States.
Porcupine Grass has seeds which are admirably adapted for burying themselves in the soil. The fruit, where it connects with the plant, has a sharp barbed point, and above this are numerous hairs pointing upward. When the seed falls with this point on the ground it is gradually worked into the earth by the movements of the hairs, due to moisture changes. Considerable injury is done to sheep by seeds, which get fast in their wool and work themselves into the flesh. Long-haired shepherd dogs are also troubled in a similar way, and when people walk through the grass the fruits stick in their clothes and cause discomfort. If eaten by-stock they work into the tissues of the mouth and throat and have even been known to perforate the walls of the stomach and intestine.
The plant is found from Manitoba to British Columbia and southward to Mexico. It is perennial, with stems three to five feet tall, and with long, narrow leaves. The narrow panicles are four to twelve inches in length, twisted below and often bent sharply. The base of the dark brown fruit is sharply pointed and densely covered with hairs.
Stipa comata Trin., is a close relative of Porcupine Grass and is quite often found in prairie hay. Its fruits produce the same effect, though to a somewhat less degree. If cut after the fruit has fallen it forms good hay.