Daldinia concentrica (Bolton) Ces. & De Not. - King Alfred's Cakes

Distribution - Taxonomic History - Etymology - Identification - Reference Sources

Daldinia concentrica

Taxonomy

Phylum: Ascomycota

Class: Soprdariomycetes

Order: Xylariales

Family: Xylariaceae

Common referred to as King Alfred's Cakes (a reference to their burnt appearance, of course, because having been given shelter by a peasant woman Alfred, preoccupied by other concerns, was reputed to have inadvertently allowed her cakes to burn, having promised that he would watch her cakes cooking. They are also referred to as Cramp Balls (because carrying them was thought to cure attacks of cramps). These hard, inedible fungi appear most often on ash and beech wood but occasionally on other hardwood trees.

Daldinia concentrica

The pinkish-brown specimens shown on the left are young and still growing, and during this asexual stage they develop over a long period and release pallid, almost colourless spores known as conidiospores (or simply as conidia), which are pinkish white when seen in mass. Once fully grown the fruitbodies turn black, like those in the picture above. At this mature stage the surface becomes dotted with tiny bumps that are the openings of perithecia, the spore-producing structures located just below the surface. Ascospores, which unlike the pallid conidiospores are jet black, are ejected from these openings in vast numbers, soon covering the surface of the fruitbody and darkening the substrate wood (creating in effect a natural spore print) for some distance around it.

The perithecia are 0.5 to 0.8mm in diameter, and their tiny openings of the surface are visible only with quite strong magnification (see below).

Daldinia concentrica

The necks of the perithecia are visible in the picture of the left; their separation is very variable. Beneath each of these tiny surface bumps these is an asci-lined flask where ascosspores develop.

Distribution

Common and widespread in Britain and Ireland and found throughout most of mainland Europe, this saprobic fungus occurs also in North America, Australia and in many other temperate countries.

Taxonomic history

Described in 1791 by British mycologist James Bolton (1750 - 1799), who gave it the scientific name Sphaeria concentrica, this ascomycetous fungus was transferred to the genus Daldinia in 1863 by Italian mycologists Vincenzo de Cesati (1806 - 1883) and Giuseppe De Notaris (1805 - 1877). Daldinia concentrica is the type species of its genus.

Daldinia concentrica spore print

Daldinia concentrica has several synonyms including Fungus fraxineus Ray, Sphaeria fraxinea With., Sphaeria concentrica Bolton, Hypoxylon concentricum (Bolton) Grev., and Stromatosphaeria concentrica (Bolton) Grev.

Etymology

Inside the fruitbody there are concentric silver-grey and black layers (pictured below), from which comes the the specific epithet concentrica.

Left: When you make a spore print of an agaricoid mushroom or of a bolete, the spores are deposited directly beneath the fertile surface - the gills or the pores. With flask fungi such as Daldinia concentrica the spores are ejected from asci buried within the stroma (fruitbody) and create a spore print extending outwards from the edge of the stroma. In this instance the spores have left a clearly visible black stain up to 3cm wide.

Identification guide

Cross-section of a King Alfred's Cake showing the concentric bands.

Fruitbody

Individual fruitbodies (formally referred to as stroma) of Daldinia concentrica are typically 2 to 8cm across, growing over several seasons (hence the growth rings), but several may merge to form a much larger compound outgrowth. Initially brown and dense, the fruitbodies soon turn black, dry out and become less dense. There is no stipe; the fruitbody is attached to the host wood by a broad, flat area underneath the cushion-shaped fruitbody. The spore-bearing surface is a series of tiny chambers called perithecia, which are embedded within the outside of the fruitbody, and ejected spores leave a slightly darker area of wood around the fungus. Each season a new fertile outer layer develops with new perithecia, inside which the next season's ascospores are produced. Large stroma are therefore much older than small ones.

Closeup of a perithecium in cross section

Perithecia

The picture on the left is a greatly magnified view of a perithecium, the dark chamber within which the asci form and spores are produced. As with other ascomycete fungi there are infertile paraphyses separating the asci.

Once the spores inside an ascus have reached maturity, the ascus expands lengthways,guided by the surrounding paraphyses, until its tip extends outside the neck of the perithecium; then water pressure built up inside the ascus bursts open the tip of the ascus and the ascospores are forcibly ejected. The ascus shrivels leaving the opening clear for the next set of eight spores to be expelled.

Ascus of <em>Daldinia concentrica</em>

Asci

Each ascus contains eight ascospores. Asci are typically 200µm x 10-11µm, cylindrical, and the asci tips are amyloid.

(Mouseover image to view a larger version of this photomicrograph.)

Spores emerging from <em>Daldinia concentrica</em>

Ascospores are ejected, mainly it seems at night, from asci hidden within perithecia just below the black surface of the fruitbody. In creating overnight spore prints I have found that some spore dust is clearly visible as far as 3cm or more from the edge of the stroma (plural stromata); however, in windless conditions a high proportion of the spores stick to one another and emerge from the necks of the perithecia in the form of contorted ropes, as seen on the left. The ropes wave about and appear to be 'growing' as more spores are added to extend them at their attachment points.

(Mouseover image to view a larger version of this photomicrograph.)

Spores of <em>Daldinia concentrica</em>

Spores

Ellipsoidal to fusiform, 12-17 x 6-9µm.

Spore print

Black.

(Mouseover image to view a larger version of this photomicrograph.)

Odour/taste

Not distinctive.

Habitat

Saprobic, on dead or dying hardwood, nearly always of ash trees. A very similar species occurs on beech.

Season

Ascospores are produced from late spring through to the end of autumn, but fruitbodies (stroma) can be seen at any time of year.

Similar species

Several blackish crust-like fungi occur on dead wood. Kretzschmaria deusta is one example; it does not have concentric rings within its fruitbody and does not form cushion-shaped or ball shaped growths.

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2011

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.

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.