Vernonia missurica Raf.

Missouri Ironweed

Vernonia missurica plant

Family - Asteraceae

Stem - To 2 m, ascending to erect, on a stout rootstock, somewhat canescent and densely hairy with spreading or bent and tangled hairs, particularly toward the tips.

Vernonia_missurica_stemUpper stem and nodes.

Leaves - Alternate, to 20 cm, lanceolate to ovate, coarsely toothed to nearly entire, upper surface usually minutely hairy, lower surface with evenly distributed, relatively long, often bent or tangled hairs.

Vernonia_missurica_leaf1Leaf.

Vernonia_missurica_leaf2Leaf abaxial surface.

Inflorescence - Irregularly branched terminal panicles, often somewhat flat-topped. Heads long-stalked.

Vernonia_missurica_inflorescencePortion of inflorescence.

Flowers - Involucre to 10 mm long, short-cylindrical to weakly hemispherical or bell-shaped, the bracts ovate to oblong-ovate, rounded or broadly angled to a bluntly pointed tip, stronly appressed, glabrous or minutely hairy, the margins usually cobwebby-hairy, usually uniformly dark purple. Florets 32-60 per head. Pappus tan to brownish purple, dimorphic, the inner bristles 6-8 mm long, the outer scales 0.6-1.0 mm long. Corollas 9-11 mm long, deeply lobed, purple.

Vernonia_missurica_involucreInvolucres.

Vernonia_missurica_floretsFlorets.

Fruits - Achenes narrowly oblong, 6-8 mm long, not flattened, with 8- 10 relatively narrow ribs, usually hairy, at least along the ribs, grayish brown to brown.

Vernonia_missurica_fruitsFruits.

Flowering - July - September.

Habitat - Streambanks, bottomland forests, swamps, prairies, old fields, disturbed areas.

Origin - Native to the U.S.

Other info. - This is one of several fairly common ironweeds found in Missouri. It can be distinguished from the others by its many (>30) florets per head, hairy leaf undersides, and strongly appressed involucral bracts. The last character is important for the identification of any Missouri ironweed, with the appressed bracts in this case serving as a counterpoint to the recurved bracts found in V. baldwinii. Vernonia missurica can be somewhat difficult to distinguish from V. gigantea, as both of these have appressed bracts.

The Missouri ironweeds hybridize freely, giving rise to intermediate forms which reflect their parentage in a huge array of morphological expression. In many areas, it is more common to find hybrid forms than it is to find plants conforming to a single species description.

Photographs taken at Tyson County Park, St. Louis County, MO, 8-31-2018 and 9-4-2018 (SRTurner).



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