Silphium perfoliatum. Cup Plant is a large branching perennial from the tallgrass region of the U.S. and Canada. It gets its name from the “cup” that is formed by the adjoined, opposite leaves on the stems. Plants can reach nearly 8 feet tall and produce numerous yellow flowers in summer. The extremely deep, large roots make it difficult to transplant once established. Prefers medium to moist soils. Recommended for pollinator and naturalized gardens as well as prairie plantings. Flowers attract butterflies, honey bees and wild bees.