Horseweed

Horseweed, Mare's tail, Canada Horseweed

[Conyza canadensis (L.) Cronq.]

Asteraceae (Sunflower Family)

▲ ▼ young plants

▲ ▼ mature plants

▲ ▼ flowering plants

▲ ▼ flowering upper portion of plant

▲ flower detail

▲ vacant lot with many mature plants

▲ prairie restoration with many horseweed plants near its border

▲ ▼ mature, flowering and post-flowering plants starting to release seeds

▲ ▼ drying, post-flowering plants in the autumn

Conyza canadensis (L.) Cronq., Horseweed, Marestail: (Bayer Code: ERICA; US Code COCA5)

U.S. native summer annual that grows 2-7 feet tall
Usually unbranched (unless mowed or grazed), and stems and leaves are covered with fine hairs that stand out from the stems/leaves
Leaves alternate, lanceolate, narrow, with a few teeth along the margins and a pointed tip; leaves often look wilted or droopy, particularly in heat of summer or on warm, windy days
A large, much-branched panicle of small, white flower heads is produced at the top of stems; head flowers don’t open very much
After flowering, white pappus (“parachutes") emerge from flower heads to carry attached seed in the wind
Horseweed may be allelopathic--where it is established, little else grows
Several populations have been indentified in U.S. that are resistant to common herbicides
Is invasive; reproduces rapidly by seed
Grows in cultivated fields, pastures, urban areas