Cyclachaena xanthiifolia (Giant Sumpweed)

Plant Info
Also known as: Marsh Elder, False Ragweed
Genus:Cyclachaena
Family:Asteraceae (Aster)
Life cycle:annual
Origin:native
Habitat:part shade, sun; moist soil; disturbed or waste areas, along shores
Bloom season:August - October
Plant height:2 to 6 feet
Wetland Indicator Status:none
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: panicle

[photo of flowers] Dense, branching clusters (panicles) at the tip of the main stem and arising from leaf axils in the upper plant. Flowers are 1/8 inch across, disk-shaped, mostly face down, petal-less with 8 to 20 greenish white to yellow disk flowers clustered in the center with 5 short, thread-like pistils around the outer edge of the disk. 5 broad, hairy and sharply pointed bracts cover the receptacle.

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

[photo of leaves] Leaves are 2 to 7½ inches long and 1 to 5½ inches wide, opposite in the lower plant with a few alternately arranged near the flowers, broadly egg-shaped with a pointed tip, long stalked, and typically shallowly 3-lobed. Upper leaves are smaller, more lance-shaped, and typically unlobed. The upper surface is rough textured, the lower silky soft, the leaf edges of young plants often finely toothed becoming coarsely toothed by mid-season. Stems are unbranched except in the flower cluster, hairless in the lower plant but with fine sticky hairs up into the panicle.

Notes:

Few annuals attain the stature of Cyclachaena xanthiifolia, commonly spelled C. xanthifolia (including by MNDNR) and formerly known as Iva xanthifolia. What appear as empty open spaces in the spring can completely fill in with these robust growers by late summer. Of two other similar species that come to mind, Annual Sunflower (Helianthus annua) has a very similar leaves on seedlings and young plants but the leaves stay finely toothed and unlobed throughout the season, and large showy, yellow flowers easily distinguish it later on in the summer. Giant Ragweed (Ambrosia trifida) also produces a similar profile, especially at a distance, but its tri-lobed leaves are more deeply lobed with persistent finely toothed edges and its flower clusters are unbranched. Like Annual Sumpweed (Cyclachaena annua), another midwestern species that does not range into Minnesota, and the ragweeds, Giant Sumpweed produces copius amounts of highly allergenic pollen in late summer as well as causing contact dermatitis in sensitive people.

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More photos

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

Comments

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

Posted by: Half Solem - Leech Lake Township
on: 2018-07-31 20:32:51

Thanks, this is it. Giant sumpweed.

Posted by: bruce honnigford - Minnetonka
on: 2018-08-03 13:44:45

Found a 5' plant and a smaller one growing in unused marshy land NE corner of I-394 and I-494.

Posted by: Bill Reynolds - NW Pennington County
on: 2018-08-11 15:02:19

The Sumpweed is blooming now (Aug) and my Honey Bees are all over it collecting pollen.

Posted by: debbie johnson - St. Louis Park
on: 2018-08-18 07:19:27

I've observed them growing in graveley soil along a Meadowbrook Golf Course utility path.

Posted by: Gene Danneman - Battle Lake, Ottertail County
on: 2019-07-12 06:23:55

Hundreds of sumpweeds germinated when an old farm yard was tilled to establish a pollinator plot. The seeds were at least 14 years old or older. The area had been mowedfor 12 years with no sign of this weed.

Posted by: Amanda - Pennington County
on: 2019-08-23 22:36:03

Found one growing in Thief River Falls.

Posted by: Mike Magnuson - Sturgeon Township, St Louis County
on: 2019-09-07 18:14:09

Volunteer plant in small flower bed. Verified via photos by Minnesota Naturalists Facebook Group.

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