Scientific Name: Ambrosia trifida

Common Name: great ragweed

Other Common Names: giant ragweed

Habit: This erect summer annual flowers from July through September.

Leaves: The opposite leaves are palmately lobed with 3 lobes, although it may occasionally have 5, or be simple. Each lobe is lanceolate shaped, and have toothed margins. The lower leaves are more deeply lobed, while the upper leaves tend to be simple. Both the leaves and the stem are rough and hairy

Identifying Characteristics: This plant can be differentiated by it's opposite leaves, and its crown shaped achene.

Flower Seed Head: The small greenish flowers occur in long racemes, and are divided by male and female flowers. The male flowers occur on the ends of long racemes, while female flowers are found at the base of the racemes, and at the leaf axils.

Seed Fruit: Each seed is enclosed in a 6 to 12 mm long black achene. The achene is crown shaped, with a long central spike surrounded by 5 shorter points.

Where Found: This plant prefers moist soils in full sun or light shade. It can be found growing in ditches, low lying fields, and other areas that tend to collect water. In dry conditions, or in poor soils, the plant will be smaller and somewhat wilted.

  • Life cycle: summer annual

  • Milky sap: Not Present

  • Plant type: Herb

  • Thorns: Not Present

  • Plant family: Asteraceae

  • Leaf arrangement: opposite

  • Leaf shape: lance

  • Leaf margin: serrated

  • Ochrea: Not Present

  • Stem hairs: has hairs

  • Flower color: green

  • Growth habit: upright and nonwoody

  • Stem: round or oval

  • Leaf structure: simple

  • Leaf hairs: has hairs

  • Root structure: fibrous; taproot

  • Flower symmetry: bilateral symetry

  • Flower diameter: dime; pencil

  • Leaf stalk: shorter than leaf