A group of tall, stately plants known collectively as Silphiums bloom in Wisconsin prairies in Augustâthey are compass plant, cup plant, prairie dock and rosinweed. Some get up to eight to ten feet tall and all of them have bright yellow flowers. They have special features that allow them to thrive in hot, dry prairies. In his book, A Sand County Almanac, Aldo Leopold described the difficulty of trying to dig up a Silphium in order to transplant it because of the very deep roots.