Description: This native perennial plant is 2-6'
tall and unbranched or sparingly branched in the upper half. The central stem
is light green, slightly pubescent, and stiffly erect. The alternate leaves are
up to 8" long and ¾" across. They are linear to narrowly lanceolate,
sessile or short-petioled, mostly hairless, and
sparingly toothed along the margins.
Each leaf has a prominent central vein. The central stem terminates in one or
more corymbs of flowerheads that are rather flat-topped. Each flowerhead spans
1/3–1" across, consisting of 50-100 magenta disk florets, no ray florets,
and numerous light green floral bracts at its base. These floral bracts are
narrowly linear or filiform (thread-like) and more or less curved; the tips of
some bracts may be colored pale purple. Each tiny disk floret has a tubular
corolla with 5 slender lobes and a divided style. The branches of each corymb
are light green and finely pubescent. The blooming period occurs during the
late summer to early fall and lasts about a month. There is no noticeable
floral scent. During the fall, each disk floret in a flowerhead is replaced by
a small achene that is bullet-shaped and often finely pubescent. At the apex of
each achene, there is a small tuft of pale purple hairs or bristles. These
achenes are distributed by the wind. The root system often produces vegetative
clumps of plants.
Cultivation: In
Illinois, this plant occurs at sites with full sun, mesic conditions, and a
loam or clay-loam soil.
Range &
Habitat: Great Ironweed is a very rare plant in Illinois; it has
been collected only in Champaign County in the east-central portion of the
state during 1957-1958 (see
Distribution
Map). These specimens are located in the herbarium of the Illinois State
Museum. Apparently, this site has been destroyed and the species was thought to
be extirpated from the state. However, during the late summer of 2005 the
webmaster discovered one or two plants of Great Ironweed at Meadowbrook Park in
Urbana, Illinois (also in Champaign County). Habitats of this rare species in
Champaign County include roadside fencerows and prairies. Great Ironweed is
more common in areas that lie to the southwest of Illinois (e.g., Missouri and
Arkansas).
Faunal Associations:
Various long-tongued bees, butterflies, and skippers visit the flowers for
nectar; long-tongued bees and some short-tongued bees also collect pollen. One
of these bees, Melissodes vernoniae, is an oligolectic visitor of
Vernonia spp. (Ironweeds). Ironweeds also attract their own special
aphid, Aphis vernoniae, which sucks juices from the stems and undersides
of the leaves. The caterpillars of various moths feed on Ironweeds (see the
Moth Table for a listing of
these species). Birds make little use of the seeds, while the bitter foliage of
Ironweed is usually avoided by mammalian herbivores.
Photographic
Location: A prairie at Meadowbrook Park in Urbana,
Illinois.
Comments: This is one of
the easier Vernonia spp. (Ironweeds) to identify because of the
distinctive appearance of the floral bracts (long and thread-like). No other
Ironweed has this kind of floral bract at the base of the flowerheads. Great
Ironweed also differs from other Ironweeds by its narrow leaves and the large
number of disk florets (50-100) in each flowerhead. Other Ironweeds have
flowerheads with fewer disk florets (20-50) and their flowerheads are less
wide. Other common names of Vernonia arkansana that are occasionally
used include 'Ozark Ironweed' and 'Curlytop Ironweed.' An alternative
scientific name for this species is Vernonia crinita. I am happy to see
this wonderful wildflower back in the state again.