Eryngium aquaticum is a species of flowering plant in the family Apiaceae known by the common name rattlesnakemaster,[4] marsh rattlesnake master,[2] corn-snakeroot, bitter snakeroot, and marsh eryngo.

The inflorescence contains white to blue flower heads with spiny, blue-tinged bracts.

[5] In the wild this plant grows in wet soils, such as those by bogs, marshes, and ditches.

[5] This plant had a number of medicinal uses for Native American groups.

[5] However, most plants sold under the name E. aquaticum are actually specimens of Eryngium yuccifolium.