Aster family (Asteraceae)
Description: This native perennial plant is about 4-10' tall and remains unbranched, except for the panicle of flowering stems near the apex. The central stem is thick, hairless, and four-sided. The large opposite leaves are up to 8" long and 5" across, which join together around the central stem to form a cup that can hold water, hence the name of the plant. These leaves are broadly lanceolate to cordate, coarsely toothed, and have a rough, sandpapery texture. The yellow composite flowers bloom during early to mid-summer for about 1-1½ months. Each sunflower-like composite flower is about 3-4" across, consisting of numerous yellow disk florets that are surrounded by 18-40 yellow or pale yellow ray florets. The infertile disk florets protrude somewhat from the center and are rather conspicuous, while the ray florets are fertile. The latter produce thin achenes, each with a well-developed marginal wing, which are dispersed to some extent by the wind. The root system consists of a central taproot, and abundant shallow rhizomes that help to spread the plant vegetatively, often forming substantial colonies.
Cultivation: The preference is full or partial sun, and moist loamy soil. This plant may drop some of its lower leaves in response to a drought. Sometimes, the leaves and buds of distressed plants turn brown, growth becomes stunted, and blossums abort in response to disease or drought. Another problem is that Cup Plant may topple over during a rainstorm with strong winds, particularly while it is blooming, or situated on a slope.
Range & Habitat: Cup Plant occurs throughout Illinois, except for a few southern counties. It is fairly common. Typical habitats include moist black soil prairies, moist meadows near rivers, low-lying woodland edges and thickets, fens and seeps, lake borders, fence rows, and along ditches near railroads.
Faunal Associations: Long-tongued bees, butterflies, and skippers are common visitors and the most important pollinators of the flowers. Some short-tongued bees, wasps, bee flies, and other kinds of flies also visit the flowers for pollen or nectar. The larvae of an Antistrophus sp. (Gall Wasp sp.) feed within the stems of this plant, and may attract the hyperparasitic wasp Eurytoma lutea. Various birds, especially goldfinches, are very fond of the seeds, and drink water from the cups formed by the leaves. Because of the tendency to form dense colonies, this plant provides good cover for birds, which often lurk among the leaves during the heat of the day, searching for insects or pausing to rest. Large herbivores, especially cattle, may eat the eat leaves of Cup Plant, especially those of immature plants.
Comments: This is an imposing, but attractive plant when it is in bloom. Cup Plant is easy to distinguish from other Silphium spp., as well as various sunflowers, by the perfoliate leaves that can hold water, and the hairless four-angled stems.