Xylaria polymorpha (Pers.) Grev. - Dead Man's Fingers

Phylum: Ascomycota - Class: Sordariomycetes - Order: Xylariales - Family: Xylariaceae

Xylaria polymorpha - Dead Man's Fingers

Xylaria polymorpha appears throughout the year at the base of beechwood stumps and occasionally on other buried hardwoods. Dead Man's Fingers is a very apt common name for this dull-looking species, which usually arises in tufts of three to six fingers that are often bent and give the impression of arthritic black knuckles.

Often appearing in palmate bunches, the stromata comprise white infertile finger-like forms with a black coating containing the flasks within which the asci (singular ascus) produce their spores. Known as 'flask fungi', these black compound fruitbodies are difficult to spot in dark woodlands.

Xylaria polymorpha - Dead Man's Fingers - close-up of the surface

Distribution

A fairly common species in Britain and Ireland, Xylaria polymorpha is found also throughout mainland Europe and in many parts of North America.

Taxonomic history

The basionym (original scientific name) Sphaeria polymorpha was given to this ascomycetous fungus in 1797 by Christiaan Hendrik Persoon.

Over the years this morbid-looking fungus has acquired many other scientific names (synonyms) including Hypoxylon polymorphum, (Pers.) Mont., Xylaria corrugata Har. & Pat., Xylaria obovata (Berk.) Berk., and Xylaria rugosa Sacc. Its currently accepted name Xylaria polymorpha dates from 1824, when Scottish mycologist and illustrator Robert Kaye Greville (1794 - 1866) transferred it to the genus Xylaria.

Xylaria polymorph, brown fruitbodies in between their asexual and sexual reproductive phases

Etymology

A close-up picture of the surface of an adult fruitbody is shown above, and its granular form is clearly evident; however, the specific epithet polymorpha comes not from the variable surface texture but from the many and varied forms that these fruitbodies can take. Polymorpha means, literally, in many shapes.

Concealed beneath those surface bumps are roundish chambers lined with spore-producing structures known as asci - hence these fungi belong to the phylum Ascomycota, the largest (by species numbers) section of the fungal kingdom.

Dead Man's Finger's is not generally considered to be an edible fungus.

The brownish Dead Man's Fingers shown on the left are in between the asexual and sexual reproductive phases of this ascomycetous fungus.

Xylaria polymorpha at the conidial stage

The beatiful specimens of Xylaria polymorpha shown on the left are at the conidial (asexual) spore-producing stage, when the 'fingers' often turn pale blue.

This splendid picture was taken by Andrea Aspenson in Wisconsin, USA, and is shown with her kind permission.

Many of the fungi whose lifecycles include both asexual (via conidiospores) and sexual (via either ascospores or basidiospores caused great confusion in the early days of fungal taxonomy. Several of them were given separate binomial scientific names for each of these stages, because they were thought to be quite different species. If you compare the light blue 'Dead Man's Fingers' with those in the picture at the top of this page, I think you will readily accept that this was hardly a stupid mistake but quite understandable.

Identification guide

Xylaria polymorpha on a mossy log

Description

Individual fingers vary from 1 to 3cm in diameter and are usually between 3 and 8cm long when fully developed. The surface is initially white or greyish and covered in a fine pallid powder (conidia) during the asexual stage, later becoming slightly granulated and darkening through brown to black, sometimes with greenish or bluish tinges.

Xylaria polymorpha cross-section view

Stroma and perithecia

As seen on the left, inside the fruitbody the flesh is white; it is quite hard. Near the surface are spore-producing cavities known as perithecia - visible in this picture as black dots against the white background. There is a tiny pore-like hole in the top of each perithecium, and when the asci explode and eject their spores this is their exit route to the great world outside.

Spores of Xylaria polymorpha, Dead Man's Fingers

Spores

Produced within structures known as asci (singular ascus), the ascospores are dark brown (when fully developed), smooth, fusiform (spindle-shaped) or banana shaped, and 20-30 x 5-9μm. (Ascomycete fungi generally have spores much larger than those of most basidiomycete species.)

Unusually, the spores shown here contain several guttules (oil-like drops) up to about 5μm in diameter, whereas most authorities refer to the spores of Xylaria polymorpha as containing commonly just one drop and sometimes none at all.

The asci are typically 200 x 10μm with eight spores in each ascus.

Spore print

Black.

Conidia on young fruitbodies of Xylaria polymorpha

Conidia

In common with other Xylaria species this fungus is also capable of asexual reproduction via conidiospores (often referred to as conidia), which are smaller than the ascospores, smooth, ellipsoidal and hyaline. The pale blue-grey powdery conidiospores are still visible on the tips of young fruitbodies pictured on the left; they will have been blown or washed away by the time that the ascospores are ripe, and then the surface of the 'fingers' will have become a much darker shade of brown.

Odour/taste

Not distinctive.

Habitat & Ecological role

Saprobic, and so found on or near (and connected) to the stumps of dead beech trees and, less frequently, other broadleaf tree stumps. Xylaria comes from the same Greek work as xylem, and simply means wood.

Dead Man's Fingers are indeed wood-rotting fungi, but they specialise in consuming neither the softish cellulose nor the much tougher lignin but rather the polysaccharides - glucan and other minority content compounds of timber that bind the cellulose and lignin together to form what we recognise as wood. As a result, when these and various other ascomycetous fungi have consumed what they can of a dead stump the remainder is a nutrient-rich soft mess that insects and other small creatures are able to feed upon (if other cellulose- or lignin-rotting fungi haven't found it first).

Season

Mainly seen in summer and autumn, but some fruitbodies can usually be found throughout the year. Producing ascospores in autumn and early winter.

Similar species

Xylaria longipes is similar but slimmer, smaller and less robust. Its fruitbodies are more obviously stalked clubs and they occur most often on the stumps and fallen branches of sycamore trees as well as beeches.

Xylaria polymorpha, Carmarthenshire, Wales UK

Above: Xylaria polymorpha, Cambridgeshire, England 2013.

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2016.

Dennis, R.W.G. (1981). British Ascomycetes; Lubrecht & Cramer; ISBN: 3768205525.

Breitenbach, J. & Kränzlin, F. (1984). Fungi of Switzerland. Volume 1: Ascomycetes. Verlag Mykologia: Luzern, Switzerland.

Medardi, G. (2006). Ascomiceti d'Italia. Centro Studi Micologici: Trento.

BMS List of English Names for Fungi

Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008

Taxonomic history and synonym information on these pages is drawn from many sources but in particular from the British Mycological Society's GB Checklist of Fungi and (for basidiomycetes) on Kew's Checklist of the British & Irish Basidiomycota.

Acknowledgements

This page includes pictures kindly contributed by Andrea Aspenson and David Kelly.

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