There’s no mistaking Sea holly (Eryngium maritimum) – no other plant is so blue and spiky. I only see it locally in one place, growing in the sandy soil of the Cardiff Bay Barrage, where it may originally have been introduced in a sown wildflower mix but has since made itself at home and prospered. In Flora Britannica, Richard Mabey explains that the leaves ‘are covered with a waxy cuticle, a device to help the plant retain water in salt winds and seaside sunshine’. And, despite its name and how spiky it is, it’s not related to Holly the shrub/tree but is, rather, a member of the carrot family.