Polarplant

Silphium laciniatum, the compass plant or polarplant, is a striking tall-grass prairie perennial of the Asteraceae native to the central United States. From a massive, deep, woody taproot it sends up stout, rough-hairy stems 1.5-3 m tall, bearing a sparse to copious milky-resinous sap. The large basal and lower stem leaves are deeply pinnatifid into narrow lobes, 30-60 cm long, sandpapery to the touch, and held in a near-vertical plane oriented north-south — a behaviour that gives both the common name and the legendary navigational reputation of the species among prairie travellers. Upper leaves become progressively smaller. The inflorescence is a sparse spike-like arrangement of large yellow sunflower-like heads 6-10 cm across, each with 15-35 ray florets surrounding a yellow disc; involucral bracts are broad, ovate, leafy, and pubescent. Flowering occurs from midsummer into early autumn. The species inhabits undisturbed tallgrass prairie, savannah openings, and roadsides on deep loams.