...in which we take a deep dive into the miniature world of lichens with Cumbria Lichens & Bryophytes expert Pete Martin. Embarking from the car park at Seatoller – and not wandering much further - we ask what a lichen is (a question not easily answered) and why lichens matter. Wandering up-dale towards Seathwaite, we stop at trees and walls to encounter five of the county's most recognisable lichens and observe a remarkable world of elf ears, maps, jam tarts and wine gums. Deep in the Borrowdale rainforest we consider the expansive 'second skin' lichen and bryophyte ecosystems that form on older pollarded trees, and the key role lichens play in fixing both carbon and nitrogen. Taking a long view of land use in the valley, our journey ends at the famous Borrowdale Yews, where we learn why Wordsworth's 'Fraternal Four' were never four at all, and why, in ecology, things are often more complex than they first seem.

• You can find Pete on Twitter twitter.com/onLoughrigg
• The Cumbria Lichen & Bryophyte Group can be found at bumbrialichensbryophytes.org.uk