(viii) Subterranean fungi
General notes
The adaptive habit of growing completely submerged beneath the surface of the ground has developed in all the major groups of fungi. Thus the simplest form related to the common bread-mould have taken up the character just as certain relatives of the disc-fungi (discomycetes) and of the flask-fungi (pyrenomycetes). In the higher fungi in several foreign countries even agarics, polypores and stinkhorns have become hypogeous, but in this country we have a very depauparate flora composed of some twenty-eight species of false (Basidiomycete) truffle. The following key may assist in identifying the different groups of hypogeous fungi for some of these species are of commercial value and includes the French or Perigord truffle, Tuber melanospermum Vittadini which is used as a constituent of Pâté de Foie Gras, and many of the fungi used as poor quality substitutes. There is a long folk-history surrounding truffles and they have been utilised in the production of aphrodisiacs for centuries. Seeking them out was a difficulty and has been overcome in different countries in different ways. Thus in continental Europe, pigs have been used to sniff them out but on finding them the pigs cannot eat the truffles because of a ring placed through their nose. In Dorset a particular breed of dog was developed to do the same job—the Dorset hounds.
A simple key would read as follows:—
- 1. Spores produced on basidia [2]
- Spores produced in asci [4]
- 2. Chambers throughout the inner tissue containing spores of approximately the same age [3]
- Chambers in the inner tissues containing spores found at different stages of development Hymenogaster
- 3. Basidiospores brown or greenish brown under the microscope, and black in mass Melanogaster
- Basidiospores colourless or pale honey colour under the microscope and ochraceous in mass Rhizopogon
- 4. Asci globose, irregularly arranged within the fruit-body and quickly breaking down to shed the spores Elaphomyces
- Asci globose or club-shaped and arranged in fertile areas which do not rapidly break down to shed the spores Tuber & relatives
Basidiomycetes
Rhizopogon roseolus (Corda) Fries Red truffle
Description:
Fruit-body: globular to tubiform and up to 60 mm broad, partly covered in mycelial cords, dirty white, later reddish-tawny gradually reddish and finally olive-brown, it soon becomes tawny on bruising when fresh and young.
Spores: medium sized, narrowly ellipsoid, smooth at first, hyaline then pale olive under the microscope and measuring 8-11 × 4 µm.
Habitat & Distribution: This fungus is not uncommon on the edges of paths, in pine woods just pushing up through the soil surface.
Ascomycetes
Elaphomyces granulatus Fries Harts’ truffle
Description:
Fruit-body: globose to ovoid, 20-40 mm broad, pale ochraceous, covered in small pyramidal warts, and when it is cut it shows three layers, an outer thin yellowish zone, an inner thicker compact white zone and within this a purplish black area full of spores separated into chambers by bands of sterile white tissue; the first two zones make up the ‘rind’.
Spores: spherical, blackish brown, warty, 24-32 µm in diameter; eight contained in globose asci.
Habitat & Distribution: This fungus is not uncommon in the surface layers of pine woods at the junction of needle debris and mineral soil. E. muricatus Fries is similar, but differs in the marbled flecked interior.
Tuber aestivum Vittadini English truffle
Description:
Fruit-body: subglobose except for basal flattening, up to 80 mm broad, covered in 5-6-sided pyramidal scales, dark brown to violaceous, white then greyish brown within, separated by a network of veins radiating from the basal cavity.
Spores: very large, ellipsoid, light or yellowish brown and ornamented with a prominent network, borne in two’s and sixes in subglobose asci and variable in size, 20-40 × 15-30 µm.
Plate 81. Subterranean fungi and fungus-parasites
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Habitat & Distribution: This fungus is to be found buried in the surface layers of soil in beech woods. T. rufum is smaller and smoother and the spores are not crested but simply minutely spiny.
Illustrations: R. luteolus—Hvass 322; LH 215. El. granulatus—Hvass 325; LH 49. T. aestivum—LH 43. Melanogaster variegatus—LH 215 (see [p. 243]). Hymenogaster tener—LH 215 (see [p. 243]).