Compass Plant (Plants of the Peggy Notebaert Nature Museum Grounds, Chicago, Illinois)

Compass Plant

Silphium laciniatum

Summary ⁷

Silphium laciniatum is a species of flowering plant in the aster family, Asteraceae, known commonly as compass plant or compassplant. It is native to North America, where it occurs in Ontario in Canada and the eastern and central United States as far west as New Mexico. Other common names include prairie compass plant,pilotweed, polarplant,gum weed, cut-leaf silphium, and turpentine plant. It is a rosinweed of genus Silphium.

Description ⁸

A mature specimen of this native perennial plant ranges from 6-12' tall. The central stem is thick, light to medium green, and has conspicuous white hairs. There is some branching into flowering stems in the upper part of the plant. The basal leaves are 12-24" long and about half as wide. They are covered in fine white hairs, broadly lanceolate in overall shape, but deeply lobed or pinnatifid. The leaves become much smaller as they ascend up the stem. The inflorescence is very tall and elongated, with yellow composite flowers about 3-4" across. They resemble wild sunflowers in overall size, shape, and structure. However, like other Silphium spp., the small tubular disk florets are sterile, while the ray florets are fertile. There is little floral scent. A mature Compass Plant has 6-30 of these composite flowers, which bloom during mid-summer for about 1½ months. The seeds are large-sized, but flat and light, and can be carried several feet by the wind. A large central taproot can extend 15 ft. into the ground. A resinous substance is produced by the upper stem when the plant is blooming. This plant can live up to 100 years.

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