Lead and other metals, particularly iron and copper, are toxic to many lichens. Some lichens will grow on stone bathed by lead contaminated water, but almost never directly on lead itself. The photograph here shows two lichen species doing their utmost not to grow on the lead lettering on this gravestone. Caloplaca flavescens (orange) normally grows in a circular manner, but here is working its way between the 9 and 0 to take on the symbolic shape of a hour-glass. Click on the photograph to enlarge.