Eryngium maritimum, the sea holly or seaside eryngo, is a species of Eryngium in the plant family Apiaceae and native to most European coastlines. It resembles a plume thistle in that its flower is burr-shaped, but the flowers are metallic blue rather than mauve. Protected from winds this dune plant grows to a height of 20 to 60 cm. Although widespread, it is considered endangered in many areas, such as Germany where its occurrence has been greatly reduced throughout and has become locally extinct in several districts.