Ontario Weeds: Biennial wormwood

Table of Contents

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

Name: Biennial wormwood, Artemisia biennis Willd.,

Other Names: armoise bisannuelle, Carrotweed, fausse tanaisie

Family: Composite or Aster Family (Compositae) 

General Description: Annual or biennial, reproducing only by seed.

Photos and Pictures

Biennial wormwood. A. Lower portion of plant.

B. Top of flowering stem. C. Flower heads on short branch from leaf axil.

Stems & Roots: Stems erect, little or not branched, 10-150cm (4-60in.) tall or occasionally much taller, smooth, hairless, firm; first leaves of young plant in a basal rosette, short-stalked, pinnately divided and redivided, the final divisions coarsely and sharply toothed; stem leaves similar to basal leaves but usually only once-divided with each division coarsely and sharply toothed, alternate (1 per node); by flowering time the lower stern leaves usually dying, and the basal rosette of leaves gone, only their scars remaining

Flowers & Fruit: Flower heads greenish and inconspicuous, clustered on many short branches in the axils of small leaves towards the top of the stem, forming a slender, elongate inflorescence; each individual flower head very small, about 2mm (1/12in.) across, yellowish-green, without ray florets; seeds numerous and very small. Upper leaves, stem and flower heads, and to a lesser extent the basal leaves, when crushed have an odour resembling a combination of sage and carrot. Flowers from August to October.

Habitat: Biennial wormwood occurs throughout Ontario in old fields, waste places, fence lines, meadows, around buildings, and occasionally in cultivated land.

Caution: It can cause tainted milk when eaten by dairy cows.

Similar Species: It is distinguished by its erect habit, its sharply toothed pinnately divided leaves, its numerous short clusters of tiny flower heads along the upper stem forming a slender, elongate inflorescence, and its odour of mixed sage and carrot.

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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