Late Boneset
Eupatorium serotinum
Aster family (Asteraceae)

Description: This native perennial plant is 3-6' tall. It is largely unbranched below, but forms occasional side stems toward the apex. The stems have indistinct lines of white hairs, and are generally pubescent. The leaves are primarily opposite, although the upper leaves near the inflorescence sometimes alternate. These leaves are up to 7" long and 2½" across, with petioles up to 1" long. They are lanceolate, largely hairless, with coarse serration along the margins, and there are 5 veins that diverge from the base. These leaves tend to nod downward from their petioles, and are often dark green.

The flat-topped inflorescence consists of numerous heads of white disk florets; there are no ray florets. Each flowerhead has about 12 disk florets. Each disk floret is about ¼" long, narrow and tubular, with 5 small triangular lobes at the top. There is also a long divided style that is white, which protrudes conspicuously from each floret. The blooming period occurs during late summer or early fall and lasts about a month. There is occasionally a mild floral scent. The small achenes develop flat tufts of hair and are dispersed by the wind. The root system is fibrous and rhizomatous. This plant often forms colonies by means of these rhizomes.

Cultivation: The preference is partial or full sun and moist conditions. The soil should be loamy and high in organic matter. Lower leaves sometimes discolor and fall off during a drought, otherwise this plant is subject to few problems. The size of this plant is significantly affected by moisture levels.

Range & Habitat: Late Boneset occurs in nearly all counties of Illinois, except for possibly three counties in the north (see Distribution Map). This is a common plant. Habitats include moist black soil prairies, moist meadows near rivers, swamps, areas near drainage ditches, low-lying areas along railroads and roadsides, pastures, and abandoned fields. This plant is often near sources of water, or where the water table is not far below the land surface. It is more common in disturbed areas.

Faunal Associations: The flowers are very popular with many kinds of insects, including long-tongued bees, short-tongued bees, wasps, flies, small to medium-sized butterflies, skippers, moths, and beetles. Most of these insects seek nectar, although bees may collect pollen and beetles may feed on it. In the upper photograph, are two Ailanthus Webworm Moths sucking nectar from the flowers. The caterpillars of various moths can be found feeding on various parts of this and other Bonesets, including Haploa clymene (Clymene Moth; eats foliage), Phragmatobia lineata (Lined Ruby Tiger Moth; eats foliage), Carmenta bassiformis (Eupatorium Borer Moth; bores into roots), Schinia trifascia (Three-Lined Flower Moth; eats flowers and seed capsules). Mammalian herbivores rarely consume this plant because of the bitter foliage. In overgrazed pastures, Late Boneset often becomes more common because of reduced competition from other plants.

Photographic Location: The photographs were taken along a drainage ditch in Judge Webber Park in Urbana, Illinois.

Comments: The delicate flowers of Late Boneset closely resemble the flowers of other Bonesets, such as Eupatorium altissimum (Tall Boneset) and Eupatorium perfoliatum (Common Boneset), in both color and structure. These Bonesets can be distinguished readily from each other by an examination and comparison of their leaves. Tall Boneset has leaves that are pubescent, more narrow, and less coarsely serrated than Late Boneset, while Common Boneset has leaves that wrap around the stem and are without petioles.

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