Here is another cool lichen genus! The Caloplaca are orange crustose lichens that forms nubbly patches on exposed rocks. They are nitrogen-loving little organisms, so when you spot some you have a good hint that there is high nitrogen present (or so I learned on a hike last month with lichen expert Shelley Bensen). You might see it on rocks where birds like to perch and deposit their nitrogen-rich droppings. Caloplaca also is abundant along roadsides with heavy traffic, where car exhaust spews out nitrogen oxide as well as other pollutants.
Caloplaca is a crustose lichen; if you see a bright orange foliose lichen, then you’re probably looking at Xantharia. Look close, because the “leaves” of Xantharia might be very small; and they might look nubbly also, due to the presence of raised little fruiting bodies.
Flowers Of Marin 