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PROFILES OF FUNGI: AMANITA

Some 30 species of Amanita are recorded in the USA, and 24 spp. in Britain, although some of them are extremely rare. They are found in both coniferous and deciduous woodlands and probably all of them form mycorrhizal associations with tree roots, assisting the uptake of mineral nutrients from soil and thereby serving vital roles in ecosystem processes. These fungi are amongst the most spectacular and beautiful, but all of them need to be treated with extreme caution because many contain deadly toxins. Some of the common names for these fungi - such as "Destroying Angel", "Panther Cap" and "Death Cap" - indicate their extreme toxicity, due mainly to the presence of amatoxins in the fruitbody tissues.

Almost all the Amanita species show the same characteristic features, illustrated in the images below:

1. The young, unexpanded fruitbody is initially enclosed by a universal veil, but this breaks and fragments as the fruitbody expands, leaving patches on the cap, and a cup-like bulb at the base.

2. A partial veil initially encloses the gills, but this is broken as the cap expands, often leaving a thin ring of tissue near the top of the stalk (stipe).

   

   Fig. 1. Amanita muscaria, the 'Fly Agaric', seen in top view (left) and side view (right). Note the distinctive red colour of the cap, with the white remains of the universal veil. Also note the ring on the stipe and the cup-like bulb at the base of the toadstool (right). As a point of interest, note the damage to the gills in the right-hand specimen. This was caused by slugs, which often feed on fungal fruitbodies. A. muscaria is a mycorrhizal fungus, most frequently seen in late summer in the litter layer beneath birch trees (Betula spp.) but it can also form mycorrhizal associations with pine trees (Pinus spp.) in sub-tropical regions where pines, and their associated mycorrhizal fungi, have been introduced. [© Jim Deacon]

   

   Fig. 2. Close-up view of a fruitbody of A. muscaria which has not yet expanded fully. Note the fragments of the universal veil, which are easily brushed off the cap, and the distinctive bulbous base. [© Jim Deacon]

   

   Fig. 3. A species of Amanita, possibly A. phalloides (the Death Cap). This species is variable in colour, and the cap can become flattened at maturity. The stem thickens markedly towards the large basal bulb.[© Jim Deacon]

   

   Fig. 4. The same specimen as above, from a different angle.[© Jim Deacon]

   

   Fig. 5. Amanita rubescens, the 'Blusher'. This is one of the commonest Amanita species, with a reddish-brown coloured cap, pure white gills, and white or rose-coloured patches on the cap. Like most Amanita spp., A. rubescens has a conspicuous ring on the stipe (clearly seen in this image) and a bulbous base. This fungus gains its common name (the Blusher) from the fact that the base of the stem typically bruises red when scratched. A. rubescens is an ectomycorrhizal fungus, often seen in mixed woodland, especially beneath beech trees (Fagus sylvatica). [© Jim Deacon]

   The extreme toxicity of several Amanita spp. to humans is due to the presence of toxins such as amatoxins and phallotoxins within the fruitbody tissues. The amatoxins in particular can be extremely potent because they are not inactivated when they are ingested. They can bind to actin microfilamants in human cells, disrupting actin-based cellular dynamics and leading to death. As noted in Chapter 3, some of these toxins, such as phalloin (derived from toadstools of the ‘death cap’ Amanita phalloides) have become important tools in cytological research because of their ability to bind to specific cellular components such as actin. In addition to these points several Amanita spp., including the Fly Agaric A. muscoides (Fig. 1), have powerful hallucinatory properties. According to Roger Phillips (Mushrooms and other fungi of Great Britain and Europe: Pan Books Ltd., London, 1981) the Fly Agaric has powerful hallucinatory and intoxicant properties, affecting both humans and reindeer in Lapland. The intoxicant can be recycled by drinking the urine of an intoxicated person. BUT, at least one death has been attributed to A. muscaria. It is dangerous to consume any Amanita species.

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