Marsh Rattlesnake (Eryngium aquaticum var. ravenelii) is perennial with white, purple or blue spiky globe-shaped flowers. It can grow to approximately 3-5 feet tall by 1 foot wide. It will tolerate full sun to partial shade and very moist soil, as long as it is not planted in an area where it gets flooded. It's a great nectar source.
/mp