Giant Ragweed, Great Ragweed, Horseweed, Buffalo Weed
Kingdom: Plantae, Division: Tracheophyta, Class: Magnoliopsida, Order: Asterales, Family: Asteraceae, Genus: Ambrosia, Species: Ambrosia trifida · Asteraceae (Aster, Daisy, or Sunflower family) · Simple, deeply palmately lobed; herbaceous annual.
Species
Ambrosia trifida
Leaf Type
Simple, deeply palmately lobed; herbaceous annual.
Family
Asteraceae (Aster, Daisy, or Sunflower family)
Shape
Palmately 3-lobed (sometimes 5-lobed or unlobed on upper stems), with ovate to lanceolate primary lobes.
Size
Approximately 6 to 10 inches long and wide in this specimen. Fully grown leaves typically range from 4 to 12 inches long and broad.
Margin
Serrate (toothed) along the margins of each lobe.
Arrangement
Opposite leaf arrangement along lower and mid-stems, sometimes becoming alternate near the flowering top.
Rarity
Very Common
Color & Pattern
Medium to bright green upper surface with lighter green veins and petiole; paler underside. Uniform coloration with no variegation.
Venation Pattern
Palmate venation at the leaf base splitting into main veins for each major lobe, becoming pinnate within each lobe.
Texture & Surface
Scabrous (rough and raspy to the touch due to stiff micro-hairs) on both surfaces; herbaceous with a somewhat stiff, paper-like thickness.
Description
Giant Ragweed is a tall, robust native annual herb capable of growing 3 to 15 feet tall. It is characterized by its large, rough, opposite 3-lobed leaves and erect spikes of greenish, wind-pollinated flowers in late summer.
Key Features
Opposite leaf arrangement, coarse 3-lobed leaf shape with serrate edges, sandpapery leaf texture, winged petiole margins, and rough stout stems with downward hairs.
Habitat
Disturbed sites, floodplain forests, stream banks, agricultural field edges, roadsides, and moist open woods in full sun to partial shade.
Geographic Range
Native to North America (widespread across North America from Canada through the United States to northern Mexico); introduced and invasive in parts of Europe and Asia.
Condition Notes
Good condition; vivid green blade showing minor insect chewing along upper right margins and small leaf-miner or mechanical spots.
Interesting Facts
Giant Ragweed is one of the primary culprits behind severe late-summer hay fever allergies, as a single plant can produce up to a billion airborne pollen grains.
Medicinal & Uses
Historically used by Native Americans for astringent, tea, and wound treatments. It holds little modern medicinal use and is mostly viewed as an agricultural weed and allergen source.
Ecological Role
Provides food for specialized insects and seed-eating winter birds; acts as a early-successional soil cover in disturbed sites, though aggressive in fields.
Similar Species
Common Ragweed (Ambrosia artemisiifolia, which has fine pinnately compound leaves), Giant Sunflower (Helianthus giganteus, non-lobed leaves), and Boxelder maple saplings (Acer negundo, compound leaves with woody stems).
Foraging Tips
Recognizable by its sandpapery, deeply 3-lobed opposite leaves on thick hairy stems. Not recommended for human culinary consumption.
Toxicity Warning
Non-toxic to ingest, but high contact sensitivity can cause severe allergic rhinitis (hay fever) and mild contact dermatitis in sensitive individuals.