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.
Other Common Names: French weed, Stinkweed. The seeds of this plant are pungently bitter, and sickening to taste, owing to a peculiar oil. For this reason they are seldom eaten by pigs, on which such seeds have the strongest effects. Samples with accompanying complaints indicate that considerable quantities of shorts and bran have been made unfit for use as feed for pigs owing to the unpal-atableness of the Field Pennycress seeds. If eaten, the plant and seeds have the same poisonous effect as the other plants of the mustard family. On some animals this effect is less apparent than on others. It would seem, for example, that rabbits can eat the seeds with impunity. This is also true of seeds like Wormseed Mustard, small quantities of which have proved fatal to pigs. Certain other animals are similarly immune. One farmer tells of a flock of geese which he fed on mill screenings containing a large percentage of Frenchweed seeds. The geese became very fat, and presented such a fine appearance that he planned to present a number of them to friends at Christmas. On preparing one of them for the table, however, it was found that the flavour of French-weed was so strong as to render the flesh unfit for food.
Fig. 24. - Seeds of Field Pennycress - Thlaspi arvense. Five time natural size.
Needless to say the original plan for the disposition of the flock was altered.
The plant, which is another introduction from Europe, has spread to the prairies, where it is a troublesome weed. It is an erect, smooth, light green plant. The radicle leaves are petioled and lance-shaped, while those on the stem are spear-shaped. with coarse teeth and a sagittate base. The clear white flowers are one-eighth of an inch in diameter and open, as in other mustards, in a flat cluster at the end of an elongating raceme. The flat seed pods are very characteristic.
owing to the broad wings which give them a total width of about one-half inch.
The flattened, dark brown seeds are about one-twelfth of an inch in diameter, with five or six deep, loop-like grooves arising from the notched place of attachment. They are pungently bitter.