The third letter of the Ogham tree alphabet, representing the letter F and meaning "alder."
Alder is a water-resistant wood used by the ancient Celts to built underwater foundations for their lake dwellings is what is now known as Switzerland. Alder was the sacred tree of Bran, the Celtic god-king. Alder is a white wood, buts its sap is red, giving it a fiery energy. This energy gives strength, both moral and physical.