Eryngium aquaticum, commonly known as Marsh Rattlesnake Master, is a perennial herbaceous plant belonging to the Apiaceae family. This species is notable for its adaptation to wet environments and its distinctive appearance, which sets it apart from many other members of the parsley family. The plant typically grows to a height of 0.5 to 1.5 meters, forming clumps of erect stems. Its leaves are basal and cauline, often appearing somewhat leathery and rigid. The basal leaves are usually long and lanceolate, with spiny margins, while the cauline leaves are smaller and clasp the stem. The inflorescence is a characteristic compound umbel, but in Eryngium, these are typically condensed into dense, globose or ovoid heads, resembling thistles or burdock. The individual flowers are small and numerous, often a pale blue or whitish color, and are subtended by prominent, spiny bracts that contribute to the plant's overall prickly texture. The fruits are small, bristly schizocarps, typical of the Apiaceae family. Eryngium aquaticum is native to the southeastern United States, where it is found in coastal plain regions. Its natural habitat includes wet prairies, savannas, ditches, marshes, and the edges of swamps and ponds, indicating a strong preference for consistently moist to saturated soils. It thrives in full sun to partial shade. While it is adapted to wet conditions, it can tolerate periods of drier soil once established, though prolonged drought is not ideal. Cultivation requirements generally mirror its native conditions, favoring moist, well-drained soils in sunny locations. It is a hardy plant, capable of surviving a range of temperatures within its native range. Historically, plants in the Eryngium genus have been noted for various uses, though specific documented uses for Eryngium aquaticum are less common in readily accessible literature compared to some other species. Its ecological role involves providing habitat and potentially food sources for various insects and wildlife within its wetland ecosystems. The spiny nature of the plant may offer some protection against herbivores. An interesting characteristic of Eryngium aquaticum, shared with other species in the genus, is its unusual flower structure for a member of the Apiaceae family, which typically features delicate, open umbels. The dense, spiny flower heads of Eryngium aquaticum are an adaptation that likely aids in attracting pollinators and potentially in seed dispersal. The common name "Rattlesnake Master" is often applied to various Eryngium species, possibly due to historical beliefs about their medicinal properties or their resemblance to plants that were thought to repel snakes.