Aster family (Asteraceae)
Description: This herbaceous perennial plant is 2-4' tall and unbranched. The central stem is round, hairless, and white, light green, or reddish purple. The alternate leaves are up to 5" long and ½" across. They are narrowly lanceolate, narrowly ovate, or linear. Their margins are serrated, while the upper and lower leaf surfaces are hairless. The lower leaf surface also has a prominent central vein, and black dots may be present. The leaves are sessile against the stem, or they have short petioles. The central stem terminates in a flat-topped cluster of magenta compound flowers (i.e., a corymb). This flower cluster is quite dense, rather than loose and spreading. The flowering stalks may be slightly pubescent.
A compound flower consists of 15-30 disk florets with a short cylinder of green bracts underneath. These bracts are appressed together like fish scales, and they are often slightly ciliate. The cylinder of bracts spans about 1/5" across. A disk floret is magenta, with 5 spreading lobes and a prominent divided style. The blooming period occurs from late summer to early fall, and lasts about a month. There is no noticeable floral scent. The flowers are replaced by achenes that have a pappus of hair-like scales. These achenes can be blown several feet from the mother plant by gusts of wind. The root system is spreading and fibrous.
Cultivation: The preference is full sun, moist conditions, and fertile soil. Partial sun and slightly moister or drier conditions are also tolerated. This plant can withstand occasional flooding for short periods of time. The foliage is not bothered by pests and disease to any significant extent.
Range & Habitat: The native Smooth Ironweed is fairly common in in the northern half of Illinois, but uncommon elsewhere in the state (see Distribution Map). Habitats include wet to moist black soil prairies, riverbottom prairies, marshes, sloughs along railroads, and edges of fields. Smooth Ironweed is found in wetland habitats to a greater extent than other species of Ironweeds.
Faunal Associations: The flowers attract long-tongued bees, butterflies, and skippers primarily. Other visitors include bee flies and Halictid bees. These insects seek nectar, although bees also collect pollen. Among the long-tongued bees, are such visitors as bumblebees, Epeoline cuckoo bees, Miner bees, and large Leaf-Cutting bees. An oligolectic bee of Ironweeds is Melissodes vernoniae. The caterpillars of several moths feed on Ironweed, including Grammia parthenice (Parthenice Tiger Moth) and Perigea xanthioides (Red Groundling). Caterpillars that bore into the roots or stems of Ironweed include Papaipema cerussata (Ironweed Borer Moth), Carmenta bassiformis (Eupatorium Borer Moth), and some Polygrammodes spp. (Pyralid Moths). The bitter foliage of Ironweed deters consumption by mamamalian herbivores – it is known as an 'increaser' because it is one of the last plants to be eaten in overgrazed pastures.
Photographic Location: The photographs were taken of plants growing in a moist prairie along a railroad in Iroquois County, Illinois.
Comments: Another common name for this plant is Common Ironweed. However, in southern Illinois, this species is not common. Smooth Ironweed is one of the smaller Ironweeds with a compact inflorescence and smooth hairless leaves. Other Ironweed species have hairy stems or leaves. An exception is Vernonia gigantea (Tall Ironweed), which has hairless leaves and stems upon occasion. However, Tall Ironweed has a spreading inflorescence, and it is usually a taller plant (as the name implies). The larger leaves of Tall Ironweed exceed ½" across, while the leaves of Smooth Ironweed are ½" or less. Some authorities state that Smooth Ironweed has black dots on the undersides of the leaves, but this is not always true. The species in this genus are occasionally difficult to identify because they can hybridize with each other.