Calicium is a genus of leprose lichen lichens. It is in the family Caliciaceae. The genus has a widespread distribution and contains 30 species. The sexual reproduction structures are a mass of loose ascospores that are enclosed by a cup shaped exciple sitting on top of a tiny stalk, having the appearance of a dressmaker's pin (called a mazaedium), hence the common name pin lichen. They are also commonly called stubble lichens. They have been used as indicator species for old growth redwood forests.