Silphium perfoliatum L.
Cup plant, Indian cup, ragged cup, carpenter weed
Cup plant, named for the cup-shaped depression formed where opposing leaves meet the stem, is another member of the very large aster family. It is a North American native.
Identification: Plants are 4-10' (1.2-3 m) tall, on single stalks that branch only near the flowering top. They could be mistaken for a type of sunflower, except for the unusual leaves. The stem is thick and hairless, four-sided, and green or purple. Leaves are opposite, joined to each other at the stems, producing a depression between them that holds water. The trapped water often attracts birds. Leaves are rough to the touch, and coarsely toothed. Flowers have a dark yellow central disk surrounded by 18-40 bright yellow petals (“ray florets”). They appear from July to October. Fruits are egg-shaped achenes ¼-½" (7.6-12 mm) long, with wings.
Silphium perfoliatum at Kansas Native Plants
Silphium perfoliatum at Illinois Wildflowers
Silphium perfoliatum at the University of Wisconsin's Robert W. Freckmann Herbarium
Silphium perfoliatum on Wikipedia
Silphium perfoliatum at the Lady Bird Johnson Wildflower Center
Silphium perfoliatum on hort.net
Silphium perfoliatum on Kansas Wildflowers and Grasses
Silphium perfoliatum at the Missouri Botanical Garden
Silphium perfoliatum on the USDA Plants Database (PDF)
Silphium perfoliatum description by Thomas H. Kent, last updated 25 May 2020.
Range: Zones 3-9: