Always take a look at the sticks and limbs that come down from old trees. There’s a lot of stuff going on up there, out of sight, and breakages provide a great opportunity to see what. This piece of an oak has at least two nice lichens on it.
Star Rosette Lichen (Physcia stellaris).
Rosette Lichen (Physcia millegrana).
Both IDs tentative. The chocolate-like disks are apothecia, where the spores are made.
From Sheldrake’s Entangled Life: “In joining forces, the fungal partners are part photobiont and the photobionts part fungus. Yet lichens resemble neither. Just as the chemical elements of hydrogen and oxygen combine to make water, a compound entirely unlike either of its constituent elements, so lichens are emergent phenomena, entirely more than the sum of their parts.”
Sheldrake continues: “The word individual comes from the Latin meaning ‘undividable.’ Is the whole lichen the individual? Or are its constituent members, the parts, the individuals? Is this even the right question to ask? Lichens are a product less of their parts than of the exchanges between those parts. Lichens are stabilized networks of relationships; they never stop lichenizing; they are verbs as well as nouns.”
Sheldrake asks the same questions about animals, since we are also networks combining microbiomes and viral and bacterial parts that originally came from elsewhere. More anon, as the mushrooms expand my mind.
Union Street. 
More marvelous lichens from Nantucket.
And amidst them, a tiny mushroom. 
Lichens are extremely sensitive to air pollution, so we don’t have all that many here in the city. We’re missing out on an amazing little universe as a result, one we’ve gotten used to not seeing. This is a perfect example of the way environmental destruction isn’t noticed: as species decline and disappear, we become used to what we see now in the present, forgetting what once was. Everything seems normal now, but isn’t, not by a log shot. 
Last week, however, I was thirty miles off the coast of Cape Cod, on Nantucket, where the frisky air is some of the cleanest on the East Coast. As a consequence, the place is a lichen wonderland. A similar habitat to Long Island, Nantucket thus serves as a window into our own past here. 
Lichens are composite, symbiotic organisms, made up of fungus and algae and/or cyanobacteria. They come in some very interesting forms. 
Lichens can grow on almost any surface. An ocean-nestled place like Nantucket means they’re thick on wood, both alive and dead (fences, houses), but higher elevations and drier places will see them on rock. The base of this hoary elm has a particular rich landscape of lichen.
Backyard and Beyond 