Dog fennel

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Code: w46
Latin name: Eupatorium capillifolium (Synonym: Anthemis cotula)
Source material: Pollen
Family: Asteraceae
Common names: Dog Fennel, Mayweed

Some sources regard Dog fennel as Anthemis cotula. Other sources refer to stinking chamomile as Anthemis cotula.

Allergen Exposure

Dog fennel is an aggressive native perennial herbaceous annual member of the Asteraceae (Composite) family native to south-eastern North America. The Asteraceae are one of the largest families of flowering plants with about 25,000 species. Twelve major tribes are recognised. Dog fennel is a member of the tribe which also contains Yarrow, Chamomile, Sage, Wormwood, Chrysanthemum and Tansy. (1)

Dog fennel is primarily a weed of landscapes, nursery, and some agronomic crops that is found throughout the United States.

Dog fennel is a winter or summer annual with finely dissected leaves that may reach between 50 cm and 2 meters in height. Stems below the cotyledons are green and become maroon with age. The first true leaves are opposite, but all subsequent leaves are alternate. All true leaves are thick and finely dissected with some short hairs. The stems and base are covered in leaves so dissected that they resemble green hairs coming out of the stem in fractal patterns. (2) The leaves are alternate, finely dissected, approximately 2 - 6 cm long and 2.5 cm wide. Leaves emit an unpleasant odour when crushed.

The flowers occur in solitary heads at the ends of branches and are approximately 2 cm to 3 cm in diameter and are white (ray flowers) with yellow centres (disk flowers). The white ray flowers have 3 distinct teeth.

Dog fennel spreads by both seeds and rootstocks and can grow quite aggressively. It is common in pastures.

In Florida, USA, Dog fennel in particular is widespread and implicated as an important pollen. Dog fennel and groundsel bush (Baccharis sp.) pollinate simultaneously, and their pollens cross-react with ragweed. (3)

Allergen Exposure

No allergens have been characterised.

Potential Cross-Reactivity

Cross-reactivity could be expected between species of the family Asteraceae. Dog fennel and groundsel bush (Baccharis sp.) are reported to cross-react with ragweed. (3)

Clinical Experience

IgE-mediated reactions

Anecdotal evidence suggests that asthma, allergic rhinitis and allergic conjunctivitis are common following exposure to pollen from Dog fennel; however, no specific studies have been reported to date.

In Tampa, Florida, the major weed pollen season (May through Dec.) was reported to consist of Ragweed, Mexican tea, Pigweed, Dog fennel, and false nettle. A minor weed season (March through July) consisted of Sorrel and Dock. (4)

Other reactions

Allergic contact dermatitis following contact with Dog fennel has been reported. (5, 6)

Compiled by Dr Harris Steinman,


  1. Lewis WH, Vinay P, Zenger VE. Airborne, and Allergenic Pollen of North America. Baltimore: Johns Hopkins University Press 1983:85-90,207.
  2. Wikipedia contributors, "Eupatorium capillifolium," Wikipedia, The Free Encyclopedia, (accessed August 22, 2008).
  3. Phillips JF, Jelks ML, Lockey RF. Important Florida botanical aeroallergens. Allergy Asthma Proc 2010;31(4):337-40.
  4. Bucholtz GA, Lockey RF, Wunderlin RP, Binford LR, Stablein JJ, et al. A three-year aerobiologic pollen survey of the Tampa Bay area, Florida. Ann Allergy 1991;67(5):534-40.
  5. Menz J, Winkelmann RK. Sensitivity to wild vegetation. Contact Dermatitis 1987;16(3):169-73.
  6. Paulsen E, Andersen KE, Hausen BM. Sensitization and cross-reaction patterns in Danish Compositae-allergic patients. Contact Dermatitis 2001;45(4):197-204.


As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.