People collect leaves? Why?
Because our teachers made us do it in elementary school and we had to place them between two pieces of paper and pile books on them to press them flat. Some people used to collect these pressed leaves in books for the duration of their lives every time the found a new species of tree, just like some others kept a life list of their bird sightings each time they sighted a new to them species of bird. And some people also pressed fairies between the pages of books to keep them for posterity as described in Lady Cottington's Pressed Fairy Book.