Invasive Plants in Minnesota

Dog Fennel is an introduced erect annual forb growing from 4 to 36 inches high on much branched stems and usually with a fetid odor and acrid taste. Stems are mostly green, sometimes with red tinges as seen below; varying from free of hair to with many short stiff hairs - sometimes glandular in the upper stem.

The leaves are alternate on the stem and pinnately divided 1 to 2 times (sometimes 3x) into narrow pointed lobes which are very thin, without hair, and stalkless in the upper stem, stalked on the lower stem. Leaves are 3/4 to 2-1/2 inches long. A foul odor is released when leaves are crushed.

The floral array is a solitary, stalked flower at the end of the stem branches, stalks up to 4 inches long.

The flower head involucre is 5 to 9 mm in diameter and the head when open is up to 1-1/4 inches wide. It is convex on top initially and then becomes oblong forming a small dome of disc florets. The head is composite with two floret types. An outer ring of 10 to 15 ray florets with white rays. Ray tips are rounded but most will show 3 teeth. These florets bear styles but are sterile. The ray florets surround a central receptacle of numerous (100+) disc florets which have yellow corollas and are bisexual and fertile. Corolla tubes are cylindric with 5 stamens tightly surrounding the central style of each floret. The outer disc florets have a very small bract. Wrapping the outside of the flower head are 3 to 5 series of green phyllaries which have whitish margins and are densely hairy.

Seed: Fertilized disc florets produce a dry brown cypsela, 1.3 to 2 mm long, with 9 to 10 ribs, often gland dotted in the rib furrows. They are without any bristly or fluffy pappus and are distributed by the wind shaking the stem and by water as the seeds are light enough to float easily. Each plant can produce thousands (up to 960,000 on large plants) of seeds which remain viable in soil for a number of years. (Ref. at bottom of text below photos). The plant spread widely in earlier times as the small seeds were frequently found as an impurity in grass and clover seed. (Ref. #6b)

Habitat: Dog Fennel sets down a taproot with many fibrous roots in disturbed sites with various types of soil, thrives in rich soils, in mostly moist conditions or where there is regular moisture applied, full sun preferred. It used to be prevalent in barn yards. In the western states it is often found in irrigated fields. It spreads by re-seeding. (Ref. Below)

Names: In older literature Dog Fennel was classified as Maruta cotula. The genus name Anthemis, refers to Chamomile and is from the Greek name anthĕmis for that plant. The species cotula, means 'small cup' in Greek and may refer to the hemisphereic shape of the flower head. The author name for the plant classification - 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. The use of the word fennel is due to the leaf resembling that of fennel, and 'dog fennel' then refers to a fennel-like plant with the foul odor, perhaps like certain wet dogs. See Eloise Butler's notes below the photos.

Comparisons: The most similar species is Anthemis arvensis, Corn Chamomile which looks very similar but the stems branch mostly in the lower section, not throughout, and the foliage does not have the fetid odor when crushed. The plant also resembles the true chamomile, A. nobilis, but that plant lacks the odor and the flowers have membraneous scales beneath and is not found in the wild in North America.