Xylaria polymorpha, commonly known as Dead Man’s Fingers, is a fascinating and easily recognisable fungus that can be found in woodlands and forests throughout the UK, Ireland, mainland Europe, and parts of North America. This saprobic fungus is known for its distinctive appearance, resembling blackened, swollen fingers emerging from the base of dead or dying trees, or from buried wood. The name “Dead Man’s Fingers” is very apt, as the fruiting bodies often appear in tufts of three to six finger-like structures that are bent, giving an impression of arthritic black knuckles.
Appearance and Structure
The fruit bodies, or stromata, of Xylaria polymorpha are typically 3-8 cm tall, though they can reach 10 cm, and 1-3 cm in diameter. When young, they are pale grey with whitish tips, but they mature to become black or brown, sometimes with shades of blue or green. The surface of the mature fruit body is slightly granulated, with a texture caused by tiny structures called perithecia. These perithecia are flask-like chambers embedded in the surface of the stroma and are responsible for producing and releasing spores.
Internally, the stroma is white and has a spike-shaped structure. The blackened dotted area surrounding the white interior is composed of the perithecia. These perithecia contain asci, which are sac-like structures that hold ascospores. The asci elongate into the ostiole, from which they discharge the ascospores outwards. The spore print of Xylaria polymorpha is black.
Life Cycle and Reproduction
Xylaria polymorpha exhibits both sexual and asexual reproductive stages. In the spring, the fungus often produces a layer of white or bluish asexual spores called conidia, which grow on its surface and the surrounding area. The conidia are powdery and can be easily dispersed by wind or water. The sexual phase involves the production of ascospores, which are dark brown, smooth, and either fusiform or banana-shaped. The asci, which hold the ascospores, are typically 200 x 10μm and contain eight spores each. The spores can take months to distribute.
The fungus begins as spores that enter openings in tree leaves, where they can remain hidden for months. Xylaria polymorpha is considered a weak pathogen that induces slow rot, giving the host tree a chance to recover. It can survive in wood remnants for up to 15 years.
Habitat and Distribution
Xylaria polymorpha is a cosmopolitan species found across all six inhabited continents. It is commonly found growing from the bases of rotting or injured tree stumps and decaying wood, particularly beech. It is often seen poking up through moss and dead leaves. Although it is commonly associated with beech trees, it can also colonize other substrates like woody legume pods, petioles, and herbaceous stems. It is a saprobic fungus that decomposes the polysaccharides in wood, leaving behind a nutrient-rich soft mess.
Taxonomy and Etymology
The scientific name Xylaria polymorpha reflects the fungus’s varied forms; the specific epithet polymorpha means “many forms”. The fungus was first described as Sphaeria polymorpha in 1797 by Christiaan Hendrik Persoon, and later transferred to the genus Xylaria by Robert Kaye Greville in 1824. Over the years it has acquired many synonyms, including Hypoxylon polymorphum, Xylaria corrugata, Xylaria obovata, and Xylaria rugosa.
Edibility and Ecological Role
Xylaria polymorpha is not generally considered an edible fungus. It plays an important role in the ecosystem by breaking down dead wood, thus returning nutrients to the soil.
In summary, Xylaria polymorpha, or Dead Man’s Fingers, is a common and easily identifiable fungus with a unique appearance and a key ecological role. Its presence in woodlands and forests is a testament to the complex beauty and functionality of the natural world.
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