Minnesota Wildflowers


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Ambrosia trifida (Giant Ragweed)

Plant Info
Also known as: Great Ragweed, Horseweed
Genus:Ambrosia
Family:Asteraceae (Aster)
Life cycle:annual
Origin:native
Status:
  • Noxious Weed
Habitat:part shade, sun; fields, along roads, edges of woods
Bloom season:July - September
Plant height:3 to 12 feet
USDA PLANTS database:Minnesota county distribution map
Spotted in Ramsey County at:

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Detailed Information

Flower: indistinct spike

[photo of flower] Narrow 3 to 8-inch spike of yellowish green flowers on short stems. Individual flowers are 1/8 inch across and have no petals. One plant may have several spikes.

Leaves: opposite lobed simple

[photo of leaves] Leaves have serrated edges and can be very large—up to 12 inches long and 8 inches wide. The largest leaves have 3 to 5 lobes with pointed tips; the smaller leaves are unlobed and pointed on both ends. Attachment is opposite.

Notes:

This plant is the cause of much suffering during hay fever season.

Where to buy native seed and plants

Help support this site by buying seeds & plants from these vendors. Tell them we sent you!

  • Prairie Restorations - Bringing people together with the land
  • Shop for native seeds and plants at PrairieMoon.com!
  • Out Back Nursery and Landscaping - Where Ecology and Horticulture Unite
  • Shooting Star Native Seeds - Native Prairie Grass and Wildflower Seeds

Map of native plant purveyors in the upper midwest

More photos

All photos taken at Long Lake Regional Park in New Brighton, MN, August 2006.

Comments

Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Elizabeth M in Lino Lakes -Anoka County
on: 2009-08-10 14:09:56

We have an abundance of this plant at our property. The property borders protected wetlands and is mostly wooded and shady with sandy soil. This particular plant grows along the tree lines.

Posted by: Alex in Proctor - southern St. Louis County
on: 2010-08-16 09:51:49

When we left for vacation two weeks ago, it was not quite identifiable or noticeable. When we got back last Sunday, it was dark. Monday arrived, and we noticed the nine-foot tall plants in our gooseberry and currant garden...seems to be this plant.

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