Sea Holly, once called Sea Eryngo or Sea Holm, is a small to medium size perennial. The flowers have pale blue dense heads surrounded by spiky, mauve bracts. The shiny bluish leaves grow in threes up the stems, and have stiff spines. The stems are stiff also and, because they come from a creeping rootstock, many of them quickly form a little bush.
The plant grows on sand, and is found in many places round the coast.
This is the only Eryngium to be found in Ireland. The Field Eryngo of Watling Street Thistle (Eryngium campestre) is very scarce in Britain and unknown in Ireland. Sea Holly is cultivated by gardeners as border plant with strong effects, as are related Eryngiums of Africa and Asian origin.
The flowers are in bloom in July and August.
Sea Holly grows on sand all round the coasts of Europe.