Lobaria pulmonaria
This lichen has the common name of tree lungwort because of the distinctive pattern of ridges and depressions on the thallus. When the thallus is wet it is a vibrant green but when dry it can become quite papery and change to brown or even red. Parts of the underside of the thallus are tomentose (covered with a felt like fungal mat) giving the very distinctive brown and white pattern which reflects the ridges on the upper surface