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Giant (Tall) Ragweed

WEEDS

GENUS/SPECIES


Ambrosia trifida

FAMILY


Asteraceae
(Compositae)

SYNONYMS


Information not available

DISTRIBUTION


Eastern two-thirds of US

  • Central Montana eastward to Maine
  • Maine southward to NW Florida
  • Florida westward to W Texas
  • W Texas N to central Montana
  • Additional population in SE Arizona

Comments

This impressive native annual weed can grow to be over 13 feet tall. It is especially abundant in wet areas such as sandbars along rivers. The larger leaves usually have 3 points, occasionally five. The plant blooms in late summer and early autumn. The numerous male flowers, which produce copious pollen, are along spikes found at the top of each branch. There are relatively few female flowers that are inconspicuous and found below the male. Allergenically, it is highly cross-reactive with short ragweed.