Moonwort (Botrychium lunaria) Upper Teesdale, County Durham
This small, unusual fern grows throughout Britain, but with a preponderance in the north. It usually grows in upland, limestone pastures. It doesn't resemble a typical fern, and gets the name Moonwort, from the crescent moon-shaped leaves up the stalk.
Its unusual appearance and scarcity made it much in demand by medieval herbalists, who thought it capable of opening locks, and removing the shoes from horses.