Giant ragweed

June 11, 2015

Ambrosia trifida L. Asteraceae (Aster family)

Life cycle

Erect, branching summer annual.

young giant ragweed plant
Young giant ragweed plant.

Leaves

Cotyledons are thick and oval to spatula-shaped and differ from those of common ragweed by being three to four times larger. Initial leaves are entire; successive leaves have three to five lobes and leaves are opposite in arrangement. Leaves are hairy and rough.

giant ragweed seedling giant ragweed leaf
Giant ragweed seedling (left) and leaf (right).

Stems

Usually hairy and rough to touch, erect and branched and up to 15 feet in height.

Flowers and fruit

Flowers are generally inconspicuous, found on terminal branches. They produce prolific amounts of pollen. The seed is enclosed in a single-seeded, woody fruit with five spikes encircling a long point, resembling a crown. Seeds are found in the axils of the upper leaves

giant ragweed flowering branch
Giant ragweed flowering branch.

Reproduction

Seeds.

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