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Weed Identification

horseweed

Family

Asteraceae

Scientific Name

Erigeron canadensis

Other Common Names:

marestail
marestail
marestail
marestail

Synonyms (former Scientific Names):

Conyza canadensis var. canadensis; Erigeron canadensis; Leptilon canadense

Habit

Seedlings bear 2 to 3.5 mm long by 1-2 mm wide ovate hairless cotyledons. The spatula shaped first leaves are hairy on the upper side and at the leaf margin. Canada Fleabane reaches heights from 7.5 to 180 cm this highly branched plant is covered with short bristly hairs. The crushed plant is said to have a carrot-like scent. Canada fleabane has a fibrous root system.

Leaves

The alternate oblong or lance-shaped leaves are 2-10 cm long. The leaves are frequently bristly haired especially near the base and are short stalked. The leaves are smaller in size toward the top of the plant. These smaller leaves can be as large as 8 cm long and 1 cm wide they are stalkless with smooth margins.

Identifying Characteristics

Flowers white to yellow 3-5 mm across, Stems with numerous branches, carrot odor to crushed leaves and stem. Leaves contain herpene an irritant to the nostrils of horses. May cause skin irritations in some people. This plant is also an alternate host to several plant pathogens i.e. aster yellows, tobacco mosaic virus, and tobacco ring spot virus.

Flower Seed Head

White ray and yellow disk florets compose the numerous flower heads measuring 3-5 mm across. The ray florets are usually hidden by the floral bracts. The numerous flower heads are crowded in to terminal clusters.

Seed Fruit

The fruit an achene bears an oblong, yellowish-brown, and flattened seed that is usually less than 2 mm long. The pappus is white to tan in color. Plants are capable of producing 10,000 seeds

Where Found

Throughout Canada and the United States in cultivated crops, pastures, and meadows.

Growth Habit

upright and nonwoody

Thorns or Spines

not present

Approximate Flower Diameter

Varies: 
pencil
dime

Dominant Flower Color

Varies: 
white
yellow
pink

Flower Symmetry

radial symmetery

Leaf Hairs

has hairs

Leaf Arrangement

alternate

Leaf Margin

serrated

Leaf Structure

simple

Leaf Stalk

none

Stem Hairs

has hairs

Stem Cross Section

round or oval

Milky Sap

not present

Root Structure

Varies: 
fibrous
taproot

Life Cycle

biennial

Ochrea

not present

Plant Type

Herb