This will be the final Tuesday page of the year and the last Tuesday page I will post for a while. I’ve thoroughly enjoyed this year of guest stars and hope you have as well. To end the year, and these weekly entries, I bring you a three-kingdoms-in-one superstar: Lobaria pulmonaria. Lung lichen. Lichens are compound organisms in which a fungus (Fungikingdom) establishes a symbiotic relationship with algae (Protista kingdom) or cyanobacteria (Monera kingdom), or, in some cases, with both. Lung lichen is one of those cases. It usually is found in old-growth forests, where it lives on rocks and treeshence another common name: oak lungs. Like real lungs, lung lichens are particularly sensitive to air pollution. The more gunk we put in the air, the fewer of these lichens will survive. Many lichens live in much more inhospitable places on Earth and provide sustenance for caribou and other creatures. No matter where they are found, lichens remind me of those carefully balanced and deeply satisfying partnerships across and within species that model life at its best.