Vernonia gigantea (Walter) Trel. ex Branner & Coville

Tall Ironweed


CC = 6
CW = 0
MOC = 47

© DETenaglia

Family - Asteraceae/Vernonieae

Habit - Perennial forb, with a stout, often short-rhizomatous rootstock.

Stems - Erect, to 2.5 m, single or multiple, branched toward the tip, minutely hairy, sometimes becoming nearly glabrous toward the base.

Vernonia_gigantea_stem.jpg Stem.

© DETenaglia

Leaves - Alternate, simple, sessile or short-petiolate. Blades 6-30 cm long, lanceolate to oblong-lanceolate and narrowly ovate, occasionally elliptic-oblanceolate, tapered at both ends, the margins sharply toothed, the upper surface glabrous or occasionally somewhat roughened toward the margins, the undersurface minutely hairy, especially along the veins, occasionally sparse, longer hairs also present along the veins.

Vernonia_gigantea_leaves1.jpg Lower leaves.

© DETenaglia

Vernonia_gigantea_leaves2.jpg Upper leaves.

© DETenaglia

Inflorescences - Terminal, irregularly branched panicles of heads.

Vernonia_gigantea_inflorescence.jpg Inflorescence.

© SRTurner

Heads - Discoid, with 13-30 florets. Involucre 3-7 mm long, short-cylindrical to somewhat hemispherical or bell-shaped, the bracts 2.0-5.5 mm long, ovate to oblong-ovate or oblong-lanceolate, rounded or broadly angled to a bluntly pointed tip, the innermost bracts rarely abruptly tapered to a minute, sharp point, appressed, glabrous or sparsely and minutely hairy, the margins occasionally also minutely hairy, purplish-tinged to uniformly dark purple, the midvein not keeled or only slightly so toward the tip.

Vernonia_gigantea_involucre.jpg Involucre.

© DETenaglia

Florets - Ray florets absent. Disk floret corollas 9-11 mm long, purple. Pappus dimorphic, tan to brownish purple, the inner bristles 5-6 mm long, the outer scales 0.2-0.8 mm long.

Vernonia_gigantea_flowers.jpg Florets.

© DETenaglia

Vernonia_gigantea_florets.jpg Florets.

© SRTurner

Fruits - Achenes 2.8-3.5 mm long, narrowly ribbed, usually hairy.

Flowering - August - October.

Habitat - Streambanks, pond margins, bottomland forests, swamps, fens, fields, pastures, ditches, and roadsides.

Origin - Native to U.S.

Lookalikes - V. missurica, V. baldwinii.

Other info. - This species can be found scattered throughout much of Missouri but is uncommon to absent in the southwestern region of the state. It is also distributed broadly within the U.S. Midwest. Although the ironweeds (genus Vernonia) are easily recognized by their heads of purple disk flowers, identification to species requires attention to detail. In V. gigantea, the involucral bracts are strongly appressed, and the number of florets in each head is relatively small, usually well under 30. The stems and leaves are also less pubescent than those of the close lookalike V. missurica. Under ideal conditions the plant can become very tall, towering over the heads of people and other species of ironweed. However, plants do not always achieve this stature, so height is not a reliable character for identification. Species of Vernonia can hybridize, and this complicates specific identification.

Although the species is not hugely showy, it nevertheless a welcome garden addition due to its great attractiveness to butterflies. The plants are a common sight in overgrazed pastures, because they are not palatable to grazing cattle. The sesquiterpene lactones present in the plants are responsible for a bitter taste and probably also confer some degree of toxicity.

Missouri's plants are assignable to ssp. gigantea, as contrasted with the ssp. ovalifolia of southern Georgia and Florida.


© SRTurner

Photographs taken off Lee Rd 54, Auburn, AL., 10-7-04 (DETentaglia); also at Onondaga Cave State Park, Crawford County, MO, 9-5-2011 and 9-11-2017 (SRTurner).