How to Identify Common Trunk Decay Fungi: The Northern Tooth

The name northern tooth, Climacodon septentrionalis, a common trunk decay fungus of urban maples, is a misnomer. The decay fungus is actually widely distributed in North America east of the Rockies and is found as far south as the Gulf states. Maples, especially sugar maple, are the most common hosts, but it is widely reported from other hardwood species such as beech, hickory, tupelo and birch.

Arborists are likely to encounter the often large, overlapping shelves of C. septentrionalis starting in summer and continuing into the fall. (Photo 1) The decay fungus produces annual brackets that are fleshy and soft when young. Basidiocarps (general term for fruiting structures of fungi that form brackets or conks) develop with multiple, overlapping caps that together often form large fruiting bodies a foot or more long and 8 to 10 inches wide. Their large size and light color make them hard to miss on an urban tree.

Identification

Field identification is relatively easy given that the white- to cream-colored brackets harbor a spore layer made up of densely packed, individual teeth or spines (Photo 2), hence the common name in part. The individual teeth are up to three-quarters-of-an-inch long and are easily seen without magnification when the brackets are turned upside down. (Photo 3) The tops of brackets are rough from dense hairs, and individual brackets are soft and somewhat watery when fresh.

The northern tooth is one of only a few decay fungi found on living trees that have a toothed spore layer and spines on multiple, shelf-like brackets. This feature also makes the fungus relatively easy to identify in the winter or spring after it initially fruits. (Photo 4) The brackets persist on infected trees, along with the toothed spore layer. However, they turn from creamy white when fresh to darker and discolored when colder weather arrives. They typically persist on the side of a tree even into the following spring.

Wound association

The northern tooth is commonly found associated with larger wounds or other defects on urban trees, and infection is usually through larger wounds on the trunk. (Photo 5) Most mycological sources list the fungus as a “heart rot,” but observations indicate it also can invade sapwood as the decay progresses with time. Decay columns in sugar maple are reported to extend as much as 12 feet above and 5 feet below fruiting structures. C. septentrionalis causes a white rot and produces black zone lines in decayed wood.

Management

Making management decisions on trees with C. septentrionalis maybe be difficult, as the decay appears to be relatively slow progressing. However, fruiting is often associated with other defects, such as codominant stems and large wounds, making some level of decay assessment a good idea to determine the need for removal or possibly additional mechanical support.

Christopher J. Luley, Ph.D., is a tree pathologist and consultant located in Naples, New York. He recently released the second edition of his book, Wood Decay Fungi Common to Urban Living Trees in the Northeast & Central United States. The updated and expanded second edition includes descriptions and photos of 50 different fungi. The field guide can be purchased at the International Society of Arboriculture’s bookstore.