What You Should Know
Xylaria polymorpha is a very distinctive species of fungus that is widely distributed throughout the deciduous forests of North America and Europe.
This mushroom 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.
This odd mushroom dons a couple of costumes in its rather long life span. When young it is pale (often bluish), with a whitish tip; the pale covering is a coating of asexual spores produced in this early stage of development. By summer, the mushroom begins to blacken, and by late summer or fall, it reaches maturity, when pimple-like, sexual, spore-producing perithecia are embedded just below the now dark brown to black surface.
Somewhere in the middle of this progressive costume change, Xylaria polymorpha does indeed look like a creepy set of "dead man's fingers." By the final stages, however, one is more likely to mistake it for something, um, left by a house cat a long time ago.
Fruiting bodies of the Xylaria polymorpha may persist for several months or even years and can release spores continuously during these time intervals.
Other names: Dead Man’s Fingers.
Xylaria polymorpha Mushroom Identification
Saprobic on decaying hardwood stumps and logs, usually at or near the base of the stump; sometimes appearing terrestrial but attached to buried wood; growing alone or, more commonly, in clusters; causing soft rot of the wood; appearing in spring and not decaying until late summer or fall.
Widely distributed and common in North America from the Rocky Mountains eastward (but see the discussion above regarding northern and southern "forms").
Immature Fruiting Body
Usually more or less club-shaped, with a bluntly narrowed, white tip; elsewhere pale to dark gray, often with a bluish or purplish zone; surface finely dusted, smooth, dry; interior flesh white and tough.
Mature Fruiting Body
4–14 cm tall; 1–3 cm thick (sometimes up to 5.5 cm thick when irregularly shaped); usually shaped more or less like a club, with a rounded tip, but often irregular (flattened, swollen toward the top or bottom, or even lobed); dark brown to black; surface dry, often finely scaly and/or pimply, and sometimes finely wrinkled; tapering pseudostem rooting into the substrate, black and fuzzy, up to 7 cm long; interior flesh white and very tough; perithecia up to about 1 mm across, spherical, submerged just below the surface.
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 Edibility
Dead Man’s Fingers are usually considered inedible, which is not surprising given their macabre appearance. However, the mushrooms may be edible when very young and still tender. At that stage, they taste mushroomy and do not cause poisoning symptoms when eaten raw in small amounts. Very few people have tried this mushroom, so it is not known whether it causes ill effects when eaten over a long period or how often someone has a bad reaction to it (even good edible mushrooms are not edible for everyone).
Xylaria polymorpha Bioactive Compounds
2-Hexylidene-3-methylsuccinic acid, aka piliformic acid, is the major metabolite produced by X. polymorpha (Anderson et al., 1985).
This compound (shown above), which was later isolated from the marine fungus Halorosellinia oceanica BCC 5149, showed moderate cytotoxicity against KB and BC-1 cell lines (Chinworrungsee et al., 2001).
Dead man’s fingers was shown to contain about 6% mannitol (dry weight), a sugar used as a diuretic agent (Snatzke and Wolff, 1987). Other compounds include 4-(3′-Acetyl-2′,6′-dihydroxy-5′-methylphenyl)- 4-hydroxy- 2-methoxybutanoic acid (globoscinic acid) and 5-(3′-acetyl-2′,6′-dihydroxy- 5′-methylphenyl)-3-methoxy- 2,3,4,5-terahydrofuran-2-one (globoscin) (Adeboya et al., 1995), and two cytotoxic cytochalasins 19,20-epoxycytochalasin Q and its deacetyl analog (Dagne et al., 1994). Of the latter two compounds, both were shown to be cytotoxic, but inactive in an HIV-protease inhibitory assay and a mechanism-based DNA damaging yeast assay.
Research has also gone into determining the optimal conditions for the production of X. polymorpha polysaccharides grown in liquid culture (Yang and Huaan, 2004).
Two new polypropionates designated as xylarinic acids A (4,6,8-trimethyl- 2,4-decadienoic acid) and B (2,4,6-trimethyl- 2-octenoic acid) were isolated from X. polymorpha fruiting bodies. Both compounds displayed significant antifungal activity against the pathogenic plant fungi Pythium ultinum, Magnaporthe grisea, Aspergillus niger, Alternaria panax, and Fusarium oxysporium, but they did not show any antibacterial nor cytotoxic effects (Jang et al., 2007).
Xylaria polymorpha Taxonomy and Etymology
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.
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.
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.
Photo 1 - Author: Michel Langeveld (Creative Commons Attribution-Share Alike 4.0 International)
Photo 2 - Author: Christine (Creative Commons Attribution 4.0 International)
Photo 3 - Author: Strobilomyces (Creative Commons Attribution-Share Alike 3.0 Unported)
Photo 4 - Author: Jerzy Opioła (Creative Commons Attribution-Share Alike 3.0 Unported)