Above: Giant Ragweed towering over Joe Pye Weed and Yellow Jewelweed in Oak Savanna in Madison, Wisconsin on August 12, 2022. The Giant Ragweed pictured above is easily over 9 feet tall.
Giant Ragweed - Ambrosia trifida (Possibly invasive)
Giant Ragweed is a native plant that likes moist, disturbed areas and can grow from 2 to 12 feet in height.
The flowerheads face downward on their stalks. The male flowers are yellow to greenish in clore with no petals. The female flowerheads form below the male flower and are nearly hidden in the leaf axils.
Giant Ragweed pollen can cause allergic reactions in people and is a contributing cause of hay fever in late summer.
Blooms: August - September.
Other names: great ragweed, horse-cane.
Above: Giant Ragweed leaf in Oak Savanna (8/12/22).
For more information on Giant Ragweed visit Wikipedia.
Or, for information on Giant Ragweed (Ambrosia trifida ) visit the: Wisconsin State Herbarium.
Above: Giant Ragweed in Oak Savanna growing next to Tall Thistle in Madison, Wisconsin (8/3/21).
Above: Giant Ragweed in Oak Savanna in Madison, Wisconsin (8/11/22).
Above: Giant Ragweed in Oak Savanna in Madison, Wisconsin (8/12/22).
Above: Giant Ragweed botanical illustration circa 1917-1926.
Above: Giant Ragweed specimen collected in Sheboygan, Wisconsin in August circa 1947.
Above: Giant Ragweed leave specimens collected in Shawano County, Wisconsin in August 17, 1964.
Above: 1913 Giant Ragweed line drawing species.
Above: Giant Ragweed line drawing from USDA NRCS, Wetland flora: Field office illustrated guide to plant species., USDA NRCS National Wetland Team.