A hart is a male red deer and the specific name 'scolopendrium' according to wikipedia, is the latin word for centipede. This is because the brown spore cases on the back of the leaves once reminded somebody of centipede's legs.
photo:bbc gardening plantfinder
Hart's tongue is a woodland fern and prefers alkaline or limey soils, or rocks including walls. So if you see it you can be fairly confident the soil is over limestone and therefore alkaline.