If you go for a wander through your local cemetery, this is one of the most common lichen you will see on old limestone headstones and grave monuments. Growing up to 10cm (4 inches) across and coming in vibrant shades of yellow and orange, the crust lichen Caloplaca flavescens is easy to spot.
The outer part of the thallus (that’s lichen for body!) has lobes and, at least in the beginning, the pattern in its centre can look a little like white dried-out mud (or, as one website described it, ‘crazy paving’) but that part later seems to disappear, leaving a single outer ring, or a series of thin arcs, that look to me almost like the outline of a rose in flower. If you look very closely, you can sometimes see the fruiting bodies (known as apothecia). These are a darker orange, disc-shaped, and tiny (up to 1.5mm across) – you might need your specs to see them.
Of course, you don’t just see this lichen in graveyards. It can be found on any calcareous rocks and walls, particularly those where birds have frequently been perching, as this lichen finds nourishment in nutrient-rich bird poo!