Ambrosia trifida L.
Common Name: GIANT RAGWEED
Coefficient of Conservatism: 0
Coefficient of Wetness: 0
Wetness Index: FAC
Physiognomy: Nt A-Forb

Ambrosia trifida habit A. A. Reznicek habit

Considered a native species, typical of river floodplains, but weedy in habit. In richer, moister soil than our other species, including moist ground near lakes and streams, fens, meadows; roadsides, farmyards, gardens, alleys, vacant lots, and other disturbed sites. Collected by the First Survey in 1837 (St. Joseph Co.), but the relative recent date of many collections, especially in the Upper Peninsula, suggests considerable expansion of range in historic time.

Plants 2 m tall are not unusual; our other two species never come close to such a height. The fruiting involucres are ca. 6–11 mm long, including a short beak below which are several stout, short, thorn-like protuberances. In our other species, the fruits are less than 5 mm long.

Locations

Allegan County
Bay County
Benzie County
Berrien County
Branch County
Calhoun County
Cass County
Cheboygan County
Chippewa County
Clinton County
Dickinson County
Emmet County
Gogebic County
Hillsdale County
Houghton County
Ingham County
Iron County
Jackson County
Kalamazoo County
Kent County
Keweenaw County
Lenawee County
Macomb County
Marquette County
Mecosta County
Monroe County
Muskegon County
Newaygo County
Oakland County
Ontonagon County
Ottawa County
Schoolcraft County
St. Clair County
St. Joseph County
Tuscola County
Washtenaw County
Wayne County

Citation:

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. December 17, 2017. http://michiganflora.net/species.aspx?id=215.