prairie ironweed

Prairie ironweed, also called smooth ironweed, is a 20″ to 55″ tall, erect, perennial forb that rises on a single stem or a clump of 2 or more stems from a stout, thickened rootstock.

The stems are erect, round, light green or reddish-purple, and unbranched below the inflorescence. The are usually hairless but are sometimes minutely hairy near the top.

The leaves are alternate, stalkless or on short leaf stalks, narrowly to broadly lance-shaped, 2″ to 7″ long, and ⅜″ to 1½″ wide. The leaf blades are tapered at the base and taper to a sharp point at the tip. The upper surface is green, smooth to the touch, and mostly hairless but may have fine short hairs near the margin. The lower surface is similar in color, hairless, and dotted with minute pitted glands. The glands appear as translucent dots when the leaf is held up to the sun or another light source. The margins are sharply toothed.

The inflorescence is a dense, branched, 1½″ to 4″ wide, flat-topped cluster (cyme) of many flower heads at the end of the stem. The flower heads within the cyme are not grouped into secondary head-like clusters.

The base of each flower head (involucre) is bell shaped, 3 ⁄16″ to ⅜″ long and ⅛″ to ¼″ high. The involucre is composed of 25 to 35 or more modified leaves (bracts) in 4 or 5 overlapping series. The involucral bracts (phyllaries) are ⅛″ to ¼″ long, and their tips are pressed closely to the involucre. They are green but usually tinged purplish along the midvein and toward the tip. They are mostly hairless on the back but sometimes have sparse, long, cobwebby hairs on the margins. The outer phyllaries are broad and scale-like. The inner ones are narrow.

Each flower head has 10 to 26 disk florets and no ray florets. The disk florets are purple and ⅜″ to 7 ⁄16″ long. They are tube-shaped at the base then separated into 5 long, widely spreading lobes. The flowers have no noticeable scent.

The fruit is a dry, brown, one-seeded, 1 ⁄16″ to ⅛″ long seed capsule (cypsela) with a modified calyx (pappus) is attached to one end. The pappus is in two series: an outer ring of 20 to 30 minute scales, and an inner tuft of 35 to 45 tan to brownish-purple, 3 ⁄16″ to ¼″ long hair-like bristles.

20″ to 55″

Reddish purple

Wet to moderate moisture. Prairies, meadows, pastures, marshes. Full sun.

July to September

Sources

2, 3, 5, 7, 24, 28, 29, 30.

Biodiversity occurrence data published by: Minnesota Biodiversity Atlas (accessed through the Minnesota Biodiversity Atlas Portal, bellatlas.umn.edu, 7/19/2025).

Native

Common

Subfamily
The tribe Vernonieae was formerly placed in the subfamily Cichorioideae, one of just two subfamilies of Asteraceae. It has been shown that Cichorioideae does not include all of the descendants of a common ancestor and is therefore invalid (paraphyletic). Recent molecular studies of the family Asteraceae proposed several new subfamilies. The Global Compositae Database currently recognizes fifteen subfamilies of Asteraceae, and places the tribe Vernonieae in the subfamily Vernonioideae. The placement has been widely but not universally accepted.

Some sources recongize a western subspecies Vernonia fasciculata ssp. corymbosa or variety Vernonia fasciculata var. corymbosa, including Manual of Vascular Plants (Gleason and Cronquist, 1992) (as Vernonia fasciculata var. nebraskensis), Steyermark’s Flora of Missouri (Yatskievievyck, 2006), USDA PLANTS, GBIF, NatureServe, and World Flora Online.

Other sources do not recognize any subspecies or varieties, include GRIN, Flora of North America, ITIS, NCBI, Plants of the World Online, and The Global Compositae Database.

Wildflower

Plant

Inflorescence

Inflorescence

Inflorescence

Leaves

Inflorescence

Stem

Stem

Minnesota Native Plant - Bunched Ironweed (Vernonia Fasciculata)
MNNativePlants

Ironweed (Vernonia fasciculata)
PrairieMoonNursery

Dan W. Andree
7/18/2025

Location: Dalby WMA, Norman Co. Mn.