Kretzschmaria deusta, commonly known as brittle cinder, is a fungus and plant pathogen found in temperate regions of the Northern Hemisphere. It is common on a wide range of broadleaved trees including beech (Fagus), oak (Quercus), lime (Tilia), and maple (Acer). It causes a soft rot, breaking down both cellulose and lignin, and decays the trunk and/or roots of living trees. The fungus continues to decay wood after the host tree has died, making K. deusta a facultative parasite. The resulting brittle fracture has a ceramic-like fracture surface. Black zone lines can be seen in cross-sections of wood infected with K. deusta.