Horseweed (marestail)

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

Life cycle

Erect winter or summer annual.

Leaves

Cotyledons are egg- to spatulashaped 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.

horseweed rosette
Horseweed rosette.

Stems

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.

erect central stem of horseweed
Erect central stem of horseweed.

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 flowers
Horseweed flowers.

Reproduction

Seeds.

horseweed seedhead
Horseweed seedhead.

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