Silphium terebinthinaceum is a member of the Asteraceae, a family that includes sunflowers, and is commonly referred to as prairie dock or prairie rosinweed. It is native to central and eastern North America…The leaves are rough-textured, spade-shaped, and oriented vertically in a north–south direction, providing special adaptations for survival in the prairie climate. One study found that most prairie dock’s leaves were oriented within 15° of North as well as 60° away from the horizontal. The combination of north–south and vertical arrangement seems to provide a mechanism for maintaining lower leaf temperatures at midday, thus conserving water…  [Wikipedia]

Plus they are sculpturally beautiful!