Eryngium yuccifolium

Small plants

Rattlesnake Master or button snake-root is native to the tall-grass prairies of central and eastern North America. Yucca like foliage which is blue/green and waxy coated. The largish, button-like flowers are on up to 1.2m when stalks The flowers are larger than E. agavifolium, yet the flower stalks are not as tall. Sometimes that makes them easier to accommodate in a border. Once established these are very drought tolerant as they can form taproots can reach 3 meters, allowing the plant to access moisture reserves far below the surface. These are magnets for pollinators. 

The flower image is thanks to Krzysztof Ziarnek, Kenraiz, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons

Whole plant: Sesamehoneytart, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons