Eryngium planum

Eryngium planum, commonly known as blue eryngo, flat sea holly, or blue sea holly, is a species of flowering plant in the Apiaceae (carrot/parsley) family. Native to central and southeastern Europe and Central Asia, it has been naturalized in other regions and is prized for its ornamental qualities in gardens. 

Appearance: Thistle-like herbaceous perennial forming stiff, erect clumps.
Size: Grows 1–3 feet (30–90 cm) tall and 1–2 feet (30–60 cm) wide.
Leaves: Flat, unarmed (non-spiny), and heart-shaped at the base, with toothed edges. Flowers: Small, steel-blue to violet-blue conical flowerheads from June-August