Home Asteraceae Ambrosia

Ambrosia psilostachya DC.

Common Name: WESTERN RAGWEED
Coefficient of Conservatism: *
Coefficient of Wetness: 0
Wetness Index: FAC
Physiognomy: Ad P-Forb

Sandy, open, often disturbed habitats. Usually considered native west of Michigan; not collected in the state until 1902 (Emmet and Kent Cos.) and 1903 (St. Clair Co.); it was already on Isle Royale by 1910.

The fruits lack thorn-like protuberances below the beak, or at least some of them are poorly developed and blunt. The longer, denser hairs on the leaves give the plant a decidedly gray-green aspect, quite noticeable in the field, contrasting with the darker green aspect of A. artemisiifolia.

Hybrids with A. artemisiifolia are relatively widespread in Michigan, and have been named A. × intergradiens W. H. Wagner. Also perennial, the hybrid often closely resembles A. psilostachya, but tends to be intermediate in several respects, especially intermediate pubescence on the leaves. In the field, the hybrid usually exists in a clone near the parent species, making it more readily distinguished.

R. W. Smith

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Counties
Alcona
Alger
Allegan
Alpena
Antrim
Baraga
Benzie
Berrien
Charlevoix
Cheboygan
Chippewa
Clare
Crawford
Delta
Dickinson
Emmet
Gogebic
Grand Traverse
Houghton
Jackson
Kalamazoo
Kalkaska
Kent
Keweenaw
Lake
Leelanau
Luce
Mackinac
Manistee
Marquette
Mason
Mecosta
Menominee
Montcalm
Montmorency
Muskegon
Newaygo
Otsego
Ottawa
Presque Isle
Schoolcraft
St. Clair
Van Buren
Wexford

Citation:
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. March, 17, 2025
https://lsa-miflora-p.lsait.lsa.umich.edu/#/record/214