A Compass Plant on a small prairie at the
North Woods Park near my home in northeast Iowa. USA
Aster family (Asteraceae)
Description: 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.
Cultivation: The preference is full sun and moist to slightly dry conditions. A deep loamy soil is preferred for the central taproot. It takes several years for a seedling to develop into a full-sized mature plant. Mature plants are easy to maintain, resist drought, and can handle competition from other plants. If planted on a slope, there is a tendency to flop over, particularly while blooming.
Range & Habitat: This is a typical plant of black soil prairies in the tallgrass region. It often co-occurs with Andropogon gerardii (Big Bluestem). Other habitats include sand prairies, savannas, glades, and areas along railroads.