Horseweed (marestail) – Conyza canadensis

Horseweed (marestail)

Conyza canadensis (L.) Cronq.
Asteraceae (Aster family)

Life cycle

Erect winter or summer annual.


Cotyledons are egg- to spatula-shaped and hairless. Seedling leaves initially develop from a basal rosette; mature leaves are alternate and numerous, and crowded along an erect central stem. Leaves are hairy and linear to lance-shaped with smooth to toothed margins, gradually becoming smaller toward the top of the plant.


Erect, hairy central stem arises from a basal rosette, then branches to flower, reaching up to 7 feet tall. Flowering branches resemble a horse’s tail.

Flowers and fruit

Numerous clusters of small, white flower heads are found on many short branches near the top. Each seedhead is capable of producing thousands of small seeds; each seed is enclosed in a single-seeded, wind-disseminated fruit.



Horseweed plant
New horseweed flowerhead
Horseweed flowers
Horseweed rosette

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