Amethyst Sea Holly (E. amethystinum) – Growing 1-1½ feet tall, this European native is one of the most cold hardy of the genus. It has beautiful amethyst blue flowers and a somewhat straggling nature.
Mediterranean Sea Holly (E. bourgatii) – Native to Pyrenees, this variety reaches 1-2 feet and consists of lively blue-green flowers with silver bracts and white veins within its coarse, spiny leaves.
Giant Sea Holly (E. giganteum) – Also known as Miss Wilmot’s Ghost (named for English gardener Ellen Wilmot), this Caucasus native makes an excellent plant for grouping in a background, growing from 3 to 4 feet or higher. While it may require staking, its heart-shaped leaves and large flowers are worth the extra effort.
Flat Sea Holly (E. planum) – Another plant with heart-shaped basal leaves, this native to Eastern Europe grows 2-3 feet tall and produces numerous silver-blue flower heads.
Rattlesnake Master (E. yuccifolium) – A native to the eastern United States with creamy chartreuse, button-like flowers and strap-like leaves, this species reaches 2 to 4 feet tall. Its name is said to derive from the myth that these plants could cure rattlesnake bites or drive them away.
Common Sea Holly (E. maritimum) – This plant is one of the smallest, growing from 6 inches to 1 1/2 feet high.