Deoxynivalenol (DON) is a toxin found in grains infected with the fungus Fusarium graminearum and other Fusarium species. It is often called “vomitoxin” because it primarily causes vomiting in humans and livestock. Its long-term effects are mild, but it is still a very important mycotoxin because it is the most common mycotoxin found in food.
Fungus Fact Friday
Fungi produce innumerable “mycotoxins” – compounds that are toxic to humans. In mushrooms, these cause symptoms ranging from gastrointestinal upset to death (see FFF#091–100 for more). Although these are of significant concern to mushroom hunters, their impact is relatively small. The most significant mycotoxins in terms of the number of people affected are produced by molds that naturally grow on food. Over the next few weeks, I will discuss some of the most problematic food-borne mycotoxins. Topping that list are the aflatoxins, which cause liver cancer and are especially problematic for people in developing nations.
Fungi appear in the news with surprising frequency. However, many of those stories do not provide any new information. Below is a summary of what we’ve learned about fungi from August through October 2017. Read below to learn about: ballistospory, chromosome evolution, fighting fungal pathogens (in humans, bats, and bananas), psilocybin, oil-eating fungi, and more! Visit the associated links to get the full story.
If the spirit of Halloween were a mushroom, it would be Omphalotus illudens. This agaric is commonly known as the “Jack-O-Lantern mushroom” for a few good reasons. First, it is bright orange, like the pumpkins that decorate doorsteps all over the United States in October. Not only is the cap orange, but so are the gills, the stipe, and the interior. Second, the mushroom’s gills glow in the dark, especially when they are young and fresh. Furthermore, the mushroom often has a sweet smell and is poisonous. Nothing says Halloween like something that is orange, glows in the dark, smells sweet, and has a sinister side.
In late October, it is not unusual to see Halloween decorations featuring bony fingers reaching up out of a grave. The natural world has its own version of this: Xylaria polymorpha, commonly known as Dead Man’s Fingers. This macabre name is an apt description of the mushrooms, which resemble burnt and dried out fingers reaching out of the ground to grab unwitting passers-by and drag them down into the depths of the earth. You can find these morbid ascomycetes on rotting logs at pretty much any time of the year.
One day as you check your mailbox you notice a yellow smear on the entrance to your house (for example a wooden gate). After retrieving your mail, you take a closer look and see that it’s a yellow gelatinous lobed blob – Witch’s Butter! Oh no, you think, I’ve been hexed by a witch! Knowing just what to do, you run back to the house, collect a few straight pins, and stab them through the offending substance to drain its juices and kill the spell. Unfortunately, this method doesn’t work very well for two reasons. First, this blob is actually the jelly fungus Tremella mesenterica. Like all jelly fungi, it is specifically designed to survive repeated dehydration and rehydration. Second, the main body of the fungus is still living inside the wood; unless you replace the wood, the mushroom will probably reappear in the same place!
Welcome back to creepy fungus month! I’m starting off this month with a mushroom that has a creepy name but is always fun to find: The Witch’s Hat. Hygrocybe conica gets its common name from the conic shape of its cap, its orange to red color, and its tendency to bruise strongly black. Actually, this last feature is probably the most important; when the mushrooms turn completely black they really do look like tiny hats for witches! The Witch’s Hat grows on the ground in a variety of habitats and mycologists are not sure what its ecological role is.
Phaeolus schweinitzii is a common polypore that parasitizes conifer trees. Around the bases of its victims, it produces medium-sized to large mushrooms in overlapping rosettes resembling haphazardly stacked dinner plates. The mushrooms are brown and fuzzy in the center and yellow around the edges. P. schweinitzii attacks the roots and lower trunk of older trees, making them more likely to fall in a storm. Although it routinely causes headaches for foresters and homeowners alike, people in the mushroom dyeing community covet this fungus. It dyes wool various shades from bright yellow to dark green, which earned it the common name “the Dyer’s Polypore.” Other common names used for P. schweinitzii are “Velvet-Top Fungus” and “Dyer’s Mazegill” (British).
The most readily observable features of Gyroporus castaneus are its brown cap and small size. As any mushroom hunter knows, mushrooms with this combination of features are very hard to identify… unless your mushroom is a bolete. Only a handful of boletes are small when fully grown and most of those have a reddish cap. G. castaneus – commonly called the “Chestnut Bolete” because of its chestnut brown colors – is easy to identify thanks to its small size, light brown colors, and brittle hollow stipe. Once you’ve found a small brownish bolete, the classic test to identify it as the Chestnut Bolete is gently squeezing the stipe, which should feel hollow.
Entoloma abortivum is a fascinating mushroom. The mushroom produces two forms of fruitbody: an agaric form that is an umbrella-like gilled mushroom and a “carpophoroid” (mycology-speak for “aborted”) form that looks like an oddly-shaped puffball. Both of these forms are usually found near honey mushrooms (Armillaria spp.) or in places honey mushrooms are known to grow. It turns out that E. abortivum is parasitic or partially parasitic on honey mushrooms; the aborted forms are actually the mycelium of E. abortivum attacking Armillaria mushrooms. Both the agaric and aborted forms are edible, although you need to be cautious when collecting Entoloma species.
Armillaria tabescens, the “Ringless Honey Mushroom,” is out in force in my area, a sure sign that summer is drawing to a close. Field guides often note that A. tabescens is the easiest honey mushroom to identify. That is true, but it relies on you accurately identifying it as a honey mushroom. Honey mushrooms (Armillaria spp.) are typically medium-sized to large agarics that grow in dense clusters, have a partial veil that leaves a ring, produce thick black rhizomorphs, and fruit from dead or dying wood. Of those features, the only one A. tabescens displays reliably is dense clustered growth. This makes it very difficult to identify if you’re unfamiliar with honey mushrooms. Fortunately, there are not many large mushrooms that grow in dense clusters, so it’s always worth checking the Armillaria section of your field guide when you find some.