Ministry of Agriculture, Food and Rural Affairs

Ontario Weeds: Stinkweed

Table of Contents

1. Name
2. Other Names
3. Family
4. General Description
   • Photos and Pictures
5. Stems and Roots
6. Leaves
7. Flowers and Fruit
8. Habitat
9. Similar Species
10. Caution
11. Related Links

Name: Stinkweed, Thlaspi arvense L.,

Other Names: Fanweed, Field pennycress, Frenchweed, Pennycress, tabouret des champs, thlaspi des champs, monayère

Family: Mustard Family (Cruciferae) 

General Description: Annual or winter annual, reproducing only by seed.

Photos and Pictures

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

Stems & Roots: 5-60cm (2in.-2ft) 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 & Fruit: Flowers white, very small (about 3mm, 1/8in. across) in rounded clusters at the ends of branches; seedpods very flat, rounded to oval, 8-12mm (1/3-½in.) 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 (1/16-1/12in.) 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.

Similar Species: 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.

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.

Related Links

... on general Weed topics
... on weed identification, order OMAFRA Publication 505: Ontario Weeds
... on weed control, order OMAFRA Publication 75: Guide To Weed Control

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