Stinkweed, Thlaspi arvense

Life Cycle

Annual or winter annual.

Propagation

Reproducing only by seed.

Stems

5-60cm high, erect, branching in the upper part and sometimes also near the base, hairless.

Leaves

The first several leaves usually in a basal rosette at the ground surface, these with stalks and smooth or slightly wavy margins; lower stem leaves with shallow, irregular teeth, rounded towards the tip and tapering towards the narrow stalk which has 2 little lobes or auricles which clasp the stem; middle and upper leaves shallowly or sometimes deeply toothed, without stalks but with a pair of lobes at the base which strongly clasp the stem.

Flowers and Fruit

Flowers white, very small (about 3mm across) in rounded clusters at the ends of branches; seedpods very flat, rounded to oval, 8-12mm wide and usually a bit longer; the central seed-containing portion slightly thickened but surrounded by a broad flat wing with a narrow deep notch at the tip, in the centre of which are the remains of the tiny style; seed-containing section divided into 2 compartments by a very narrow septum (membranous partition), each side containing 3 to 8 seeds; this white septum often remaining on the plant after the pod breaks apart to release the seeds; seeds reddish-brown to purplish or blackish, ovoid but somewhat flattened, 1.5-2mm long with several rows of concentric ridges on each side. Flowers from early spring to late fall.

Habitat

Stinkweed occurs throughout Ontario in cultivated fields, waste places, roadsides and gardens.

Distinguishing Features

It is distinguished from the pepper-grasses, which it closely resembles, by the complete absence of hair from stems and leaves, its unpleasant odour and its larger flat seedpods with a broad flat wing.

Notes

Caution: The whole plant has a sour turnip-garlic odour which is distasteful to most people, and causes tainted milk when dairy cattle eat it.


Figure #1.

A. Base of plant. B. Flowering and fruiting stem.


Figure #2.

Stinkweed in field.


Figure #3.

Smooth stem of stinkweed.


Figure #4.

Stinkweed seedheads.


Figure #5.

Stinkweed seeds


Figure #6.

Stinkweed, with sizing.


Figure #7.

Stinkweed leaves, seedhead and flowers, with sizing.