SafePlants

Canadian Horseweed (Conyza canadensis)

Canadian Horseweed, also known as Canadian fleabane, is a common plant with a rich history and widespread distribution. The name "Horseweed" may be due to its potentially tall stature.

Common Names

• Horseweed
• Canadian Fleabane
• Coltstail
• Marestail
• Butterweed
• Canada Fleabane
• Mare's Tail

Taxonomy and Nomenclature

• Scientific Name: Conyza canadensis (L.) Cronquist
• Family: Asteraceae (also known as Compositae or the Aster family)
• Order: Asterales
• Genus: Conyza (horseweed)
• Synonyms: Erigeron canadensis. Note that Conyza canadensis (L.) Cronq. is also considered by some to be an inactive name; refer to Erigeron canadensis.
• Taxonomic Rank: Variety - Conyza canadensis (L.) Cronquist var. canadensis and Conyza canadensis var. pusilla

Distribution and Habitat

• Native to Canada and the United States.
• Now found throughout the world including Europe, eastern Russia, parts of Siberia, Central Asia, Iran, Mongolia, Japan, and China.
• Common introduction throughout the United States and Canada.
• Grows in a wide variety of habitats, including vacant lots.
• Thrives on bare soil, but is soon crowded out as perennials become established.

Morphological Characteristics

• Erect annual forb (herbaceous flowering plant).
• Grows on slightly hairy stems.
• Stems are erect, solitary, and unbranched below, occasionally branching above.
• Numerous inconspicuous flower heads about 1/8 inch across.
• Tiny white or cream-colored flowers.

Traditional Uses

• Canadian horseweed was used by numerous Native North American tribes to treat various illnesses.
• Historically used for stomach pain.

Ecological Role

• An annual that thrives on bare soil, Horseweed is soon crowded out as perennials become established.

Considerations for Pets

• Skin Contact: The text mentions that skin contact is a known hazard.

Further Information

• Encyclopedia of Life
• RHS (Royal Horticultural Society)
• Government of Canada terminology and linguistic data bank