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Purdue Landscape Report: Dead man’s fingers is an apt moniker for a gruesome-looking fungus (Xylaria polymorpha and related species) that produces club-shaped fungal fruiting bodies that appear as fingers growing around the base of dying or dead woody plants and even wooden objects in soil (Fig. 1).  With more than 25 species of Xylaria, generalizations are difficult to make (Fig. 2), but we will persevere anyways, recognizing that some Xylaria species are limited to a saprophytic existence decomposing wood (like X. polymorpha) while others, like X. mali, cause an opportunistic black root rot on apple and crabapple (Rogers, 1984; Rogers and Callen, 1986) or nothing at all (Fig. 2). Other Xylaria species infect Norway maple, honey-locust, elm and pears (flowering and edible).  Perhaps the scariest thing about dead man’s fingers is its taxonomy: X. polymorpha is an extremely variable and complicated species showing “multiple interfaces and intergradations with numerous other taxa” making speciation a challenge (Lee et al, 2000), which may explain why a crabapple with a bad graft union covered in dead man’s fingers looks otherwise healthy!

Figure 1. Dead man’s fingers is an apt moniker to describe the fruiting body of Xylaria species. Photo by Janna Beckerman.

Figure 2. Unknown Xylaria grown on fallen log. Photo by Janna Beckerman.

Symptoms and Signs

Symptoms of infection by Xylaria may appear as stress and decline, including slowed growth, dieback, premature autumn coloration and leaf drop, and even crown or structural root cankers. Apple, crabapple or pear trees infected may produce an unusually large crop of undersized fruit.

Figure 3a. Dead man’s fingers can be found associated with otherwise healthy, asymptomatic trees, or simply growing on dead wood—not necessarily causing disease.

3b. Close-up of the rootstock with multiple croppings of Xylaria on the crown. Photo by Janna Beckerman.

Signs of Xylaria are more readily identified—namely, the dead man’s fingers (Fig. 4)! The club shaped, fingerlike fruiting bodies appear singularly or as clustered “fingers” about  1- 4 inches high, often at the base of infected or dying trees, or nearby large structural roots (Fig 4).  In the spring, ascospores are produced by the “fingers”, creating a bluish bloom on the tips of the fingers. Cutting into a finger reveals a white interior with black bubbles that produce the sexual spores (ascospores).  The “fingers” can release these spores for several months or years.  In the spring, Xylaria can produce asexual spores (called conidia) anywhere on its surface, while also producing threadlike structures (called hyphae) that grow through dead or dying wood.  Xylaria can survive as hyphae in roots for up to 10 years and can spread from plant to plant via hyphae when plant roots contact each other.

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Resources:
Tree Defect Identification, The Education Store
Tree wounds and healing, Got Nature? Blog
Tree Risk Management, The Education Store
Why Is My Tree Dying?, The Education Store
The Woody Plant Seed Manual, U.S. Forest Service
Native Trees of the Midwest, The Education Store
Invasive Species, Playlist, Purdue Extension – FNR YouTube Channel
Report Invasive Species, Purdue Invasive Species
Find an Arborist, International Society of Arboriculture
Subscribe Purdue Extension-Forestry and Natural Resources YouTube Channel

Janna Beckerman, Professor of Plant Pathology
Purdue Department of Botany