Eryngium armatum is a species of flowering plant in the carrot family known by the common name coastal eryngo. It is endemic to the coastline of the northern half of California, where it along beaches and coastal bluffs. This is a low perennial herb growing patches of thick green to yellow-green leaves, each long and straight, sometimes with serrated or toothed edges. Atop stout stems are inflorescences of spiky flower heads each nearly a centimeter wide. Each is surrounded by seven or eight long, sharp-pointed bracts about two centimeters long, and sometimes more layers of bractlets on top. The tiny white to purplish flowers are tucked between the layers of bracts.