Friday, 13 January 2012

Friday Fungus: unwanted immigrants - a comment on death cap mushrooms


It would seem to me that, besides knowing which mushrooms are tasty, knowing which ones will kill you is pretty important. And mushrooms can kill you:

Lui Jun was a hardworking 38-year-old Chinese chef who made a fatal error of mistaking the toxic "death cap" mushrooms for a common edible variety used in Chinese cooking.

This was in Australia which raises an interesting point – Australia has thousands of native fungus species but the Death Cap (Amanita phalliodes) isn’t one of them. Like cane toads, rats and rabbits this particular killer arrived with the white man:

Amanita phalloides, commonly called the Death Cap, is a strikingly beautiful mushroom and the number one cause of fatal mushroom poisonings worldwide. Originally found only in Europe, it has proved to be highly adaptable to new lands and new mycorrhizal hosts.

It is our love of the good old oak tree that causes the problem – when we took oaks to North America and Australia, we carried with them traces on the Death Cap. And in California, the death cap loved its new home:


If we can assume (and trace through the literature and herbaria) that its earliest arrival in Central California was around 1938, it is remarkable to think that in a little over seven decades, Amanita phalloides can be found throughout California, from the Sierra foothills to the Channel Islands, wherever live oak is found. Death Caps have recently been documented growing with pine in Marin County (pine is its preferred host on the East Coast of North America) and with Tanoak (Lithocarpus densiflorus) in Mendocino County, and may be expanding their California tree hosts.

So – to avoid the tragic fate of those Chinese chefs, you need to know how to spot a Death Cap:


The defining features of this gorgeous mushroom are: the sacklike white volva around its base; the white ring; the white gills; the white spore print; and the smooth (rather than lined) cap margin. Cap color is not the best thing to rely on in identification, since it is fairly variable. Older specimens have a distinctive, foul smell to them, but smell is never a very objective determiner.

These mushrooms are usually (but not always) associated with oaks – but always in mixed or deciduous woodland:


Cap 6-15cm across, convex then flattened; variable in color but usually greenish or yellowish with an olivaceous disc and paler margin; also, paler and almost white caps do occur occasionally; smooth, slightly sticky when wet, with faint, radiating fibers often giving it a streaked appearance; occasionally white patches of volval remnants can be seen on cap. Gills free, close, broad; white. Stem 60-140 x 10-20mm, solid, sometimes becoming hollow, tapering slightly toward the top; white, sometimes flushed with cap color; smooth to slightly scaly; the ball-shaped basal bulb is encased in a large, white, lobed, saclike volva. Veil partial veil leaves skirt-like ring hanging near the top of the stem. Flesh firm, thicker on disc; white to pale yellowish green beneath cap cuticle. Odor sickly sweet becoming disagreeable. Spores broadly ellipsoid to subglobose, amyloid, 8-10.5 x 7-9µ. Deposit white. Habitat singly or in small groups on the ground in mixed coniferous and deciduous woods.

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