Ambrosia psilostachya (Western Ragweed)

Plant Info
Also known as: Cuman Ragweed
Family:Asteraceae (Aster)
Life cycle:perennial
Habitat:sun; disturbed soil, waste areas, dry prairie
Bloom season:July - October
Plant height:1 to 3 feet
Wetland Indicator Status:GP: FACU MW: FACU NCNE: FAC
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: indistinct Cluster type: raceme Cluster type: spike

[photo of flowers] Abundant, slender spike-like racemes, 1 to 6 inches long, at the tip of the central stem and side branches. Male (staminate) flowers are tiny, yellow to greenish and bead-like, short stalked, initially densely packed along the cluster but spreading out as the plant matures. Female (pistillate) flowers are solitary and few, typically located at the base of the cluster, along the stem or in the axils, and flanked by large leaf-like bracts.

Leaves and stems: Leaf attachment: alternate Leaf attachment: opposite Leaf type: lobed Leaf type: simple

[photo of leaves] Leaves are thick, oval-lance shaped in outline, up to 5 inches long and 2 inches wide but deeply divided into narrow lobes that are typically further lobed. Leaves are hairy, more densely on the underside and can give the leaves a gray-green cast. The lower stem leaves are oppositely attached, becoming alternate in the upper branches, stalkless or with a short stalk that is often winged. Stems are stiffly erect, may be unbranched or many branched in the upper plant, with long soft hairs when young, becoming rougher textured with age.


Tolerant of dry sandy sites and an early colonizer of disturbed soil, this native can be common in both high grade prairie remnants and disturbed urban waste places. Very similar to the annual Common Ragweed (Ambrosia artemisiifolia), which tends to be much more heavily branched, less hairy overall, has thinner, more finely divided, fern-like leaves, and is tap-rooted where Western Ragweed has fibrous, creeping rhizomes. Western Ragweed is listed in some references as Ambrosia coronopifolia.

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More photos

Photos courtesy Peter M. Dziuk taken in Anoka, Dakota and Hennepin counties.


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

Posted by: Tim Johnson - Rice Lake Sananna SNA
on: 2020-08-05 21:16:19

Just starting to bloom August 5, 2020

Posted by: gary - Moose Lake in Charlton County
on: 2022-08-03 08:35:21

A few plants along the Munger Trail.

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