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Caithness Field Club

Caithness Field Club Bulletin
2005

The Fungi in Dunnet Forest (by David Savage)
Take a walk through Dunnet forest during late summer or early autumn and you can not help but notice the fungi growing on the forest floor. This note will try to help you name some of the more prominent or easily identified species present, plus a few of the nationally uncommon or rare species to be found there.

Amongst the most prominent are groups of 5 to 10 cm (2 to 4 inches) diameter red to purple capped fungi. Pick a fresh cap and turn it over. Underneath are many radial flaps, termed gills. Try to bend a gill with the finger and it will break easily. These are members of the brittle gill or Russula family of fungi. Several different but superficially similar species of Russula are present in Dunnet forest. Notice how the gill colour varies between different groups, from deep ochre to cream and a few pure white. The gill colour of mature caps is a good guide to the different species as it reflects the colour of their spores. Spore colour is best seen by taking a spore print. Place a fresh cap, gills down, on a sheet of white paper and cover to exclude drafts. After a few hours or overnight radial lines of spores will form. As each individual spore is about 10 microns in diameter, think how many tens of thousands must be present to see them. Other differences between the species of Russula are in cell structures, mainly observable only with a microscope, or in their reactions to various chemicals.

Within Dunnet forest the most frequent purple-coloured Russula species are:
R. sardonia: with pale lemon gills, flesh uniquely turning bright pink with ammonia solution. Always with pines.
R. queletti: with cream gills, cap skin which will not peel off except at the extreme margin. Always with spruces.
R. caerulea: with deep ochre gills and often a bump in the centre of the cap. Always with pines.
R. nauseosa: with deep ochre gills, a slightly paler cap and a cap skin which will peel almost to the centre. With pines or spruces. And it does what it says in the name if eaten.
Members of the Russula family all live in a symbiotic relationship with their host trees; they grow as a sheath over the finest tree roots and extend out into the soil. The fungi extract mineral salts (including nitrate and phosphate) from the soil which they exchange for sugars with the tree. They are termed mycorrhizal fungi. They are often tied to specific host trees, even in some cases distinguishing between differing types of pines.

The Russula family are just one of the many families of fungi whose members make up the 100 or so larger fungi which can be found in Dunnet forest. Most other families have gills which are more flexible, and often their gill colour is a poor guide to spore colour. Take a small selection of different looking caps home and try making spore prints from them. Many will have white spores, but others should be chocolate or rusty brown, pale flesh pink, or even black.  Notice how the gills of some of the white-spored fungi exude small drops of fluid when damaged. Usually this is white, which gives the family its name of milk-caps or Lactarius.

The commonest representative of this family in Dunnet forest is Lactarius rufus with a 5 cm diameter red brown cap. Occasionally the much brighter rusty orange caps, again with white milk (check!), of L. mitissimus attract the eye. This has a superficial look-alike in the false chanterelle, Hygrophoropsis aurantiaca which also grows in Dunnet forest and which has shallow forked ribs under the cap and running down the top of the stem in place of the more common gills. These ribs do not contain any milk.

Also common in Dunnet forest are two milk-caps with carrot-coloured milk. The 7 cm caps are dull mottled buff, often with greenish blotches, while the undamaged gills are pale orange buff. The one with pines, and a fat pockmarked stem, is L. deliciosus (reputedly very good to eat), while L. deterrimus has a thinner, greener, stem, grows with spruce and is less good to eat.

One often plentiful fungus in Dunnet forest has a 5 to 7 cm buff coloured gently domed cap which is sticky when wet or shiny when dry. Turn the cap over and instead of gills it has a rusty ochre-coloured surface with a network of 1 mm holes (pores). The stem should have a 1 mm wide brown glutinous band (ring) about 1 cm from the top. This is Suillus flavidus,a member of the Bolete family. These differ from other fungi in both spore shape and microscopic structures. With a reputation for being rare, in practice S. flavidus is plentiful north of Inverness.

Another notable but genuinely uncommon fungus which is often present with pines near the forest workers base at Dunnet is Gomphidius glutinosus. This has a 5 to 7 cm brown sticky domed cap, a sticky white stem with a bright yellow base, and thick gills which run down the top of the stem. Its gills start white and gradually turn dark grey from almost black spores. This is also a Bolete even though it has more or less normal gills.

Many fungi are not mycorrhizal. A large number are tolerant of tannins and can live on the resources tied up in leaf litter. They are termed saphrotypes and decompose the litter and thereby recycle the nutrients.
In Dunnet forest the needle litter supports a large number of small fungi with white spores and a 1 cm diameter bell shaped cap. These are the fairy bonnets or Mycena species. Most are very hard to identify without a microscope. But look for yellow-brown caps with a sticky pale yellow stem; these are Mycena epipterygia. Also look for a fawn cap and stem, with blood red juice in the stem when fresh. Now look at the whitish gills with a hand lens. They have a narrow deep red margin formed of coloured cells on the gill edge; these are M. sanguinolenta. Worth looking out for are pale ochre caps whose white gills have a narrow yellow margin. This is the rare M. citrinomarginata which appears in small numbers most years within Dunnet forest.

Even smaller but very common in any conifer woodland is the horsehair fungus, Marasmius androsaceus. It has a Ĺ cm creamy buff cap with marked radial grooves like an old style parachute, on top of a hair-like but wiry black stem. One fruit body per needle, but linked to other needles by a black cottonlike thread. This is the mycelium, the fungi's main structure, which in most species is buried in the ground.
One important group of fungi is tolerant of the lignins in wood and consequently can break down dead wood. Dunnet forest has always had a good quantity of old wood as cut logs, and now has large areas of cut stumps as well. As a result it is a good place to see these lignicolous fungi.

The most prominent are the 5 to 10 cm diameter matt purple (but fading to ochre with sun or wind) caps of Tricholomopsis rutilans. With white spores on bright yellow gills and yellow stems they earn the name Plums and custard. They grow singly or in small groups on or near pine stumps.

Look out for occasional clusters of bright ochre 3 to 5 cm scaly caps on pine logs. With a scaly yellow stem, yellow gills and brown spores, this is Pholiota flammans, a far from common fungus in most other places.

Many of the wood-decomposing fungi grow, not in traditional toadstool shapes but as brackets projecting sideways from the wood or as crusts over the wood. Many are not easy to name.  One of the easiest and commonest grows as a small (1 to 5 cm diameter) thin (1 mm thick) crust on the wood, often with a 1 cm projecting bracket at the top. The front face is the fertile spore-bearing surface even though it is smooth rather than with the more normal gills, pores, or ribs of the toadstool-shaped fungi. The surface is a matt cream to pale fawn colour. Cut this surface with a knife or sharp finger nail and a blood-red line will appear. This is Stereum sanguinolentum, the bleeding stereum. This fungi is of further interest as it is host to a parasitic fungus, locally quite frequent but nationally rather uncommon. After a really wet spell of weather look on old spruce wood for 2 to 4 cm clumps of rather gelatinous brown ear like lobes forming a brain like mass. This is Tremella foliacea and is mostly water. When conditions dry up, the fruit body will shrink back to a pinhead sized spot.

All that remains now is to pick a pleasant late summerís day to walk around Dunnet forest and see what you can find.

Footnote 1
Other local conifer woods contain their own range of species. The mycorrhizal fungi in particular will become increasingly different to those in Dunnet forest as the soil becomes more peaty. The fungi of deciduous woodlands are of very different species.

Footnote 2
It is frequently asked if any of the fungi in Dunnet are edible. The simple answer is yes. But there are also many unpleasant ones present and quite a few that are poisonous if eaten. In Britain there are a few rather uncommon fungi that are almost inevitably fatal if eaten. There has been at least one fatality from northern Scotland from mistakenly eating one of these fungi. At least one of these potentially deadly fungi is associated with conifers and so could be present locally. So be VERY VERY SURE you know what is what before you try eating fungi from the wild. Personally I keep to the supermarket varieties.

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