Organism of the Day: Armillaria mellea

Yesterday I presented the Organism of the Day to my Biology class, and selected one of my favorites, Armillaria mellea. First, the complete classification.

Armillaria mellea (Vahl.:Fr.) Kummer (common names include: oak root fungus, honey mushroom)

Armillaria

Physalacriaceae (it was Tricholomataceae when I first learned it, but we all knew Tricholomataceae was a dumping ground for white-spored mushrooms)

Agaricales

Agaricomycetes

Basidiomycota

Fungi

Eukarya

Why should you care about A. mellea? Well, first it's an important plant pathogen, infecting hundreds of plant species, though mostly noticeable on woody species. Even though it's called oak root fungus, this is clearly a misnomer. It can also survive on dead plant material, as a saprobe.

It does produce mushrooms, being an agaric, but these are analogous to the apples on the tree, they are just a way of getting around. The mushrooms are fairly typical, with a pileus, a stipe, and a partial veil. Like most common mushrooms, the fertile part or hymenium takes the form of gills, or lamellae. The spores produced rain down and you can see deposits of them on the caps of some of the other mushrooms. Notice that it’s white, the color is an important diagnostic feature as well.It also produces structures called mycelial fans, under the bark of trees that it’s infecting, which is an important structure for feeding the organism.

But another interesting feature is the bioluminescence. This is present in many species of mushrooms (at least 70 species) and other organisms, many animals. The glow of Armillaria mellea has been observed since ancient times, and has the common name foxfire. There’s a town called Foxfire in North Carolina, and Mark Twain in mentions the boys using it in Huckleberry Finn. In some fungi, the mushrooms glow, but in Armillaria, it’s the mycelium and rhizomorphs.

Perhaps the neatest thing about Armillaria is this item. In 1992 it was reported that a single clone of Armillaria gallica was estimated to cover an area of 15 hectares (or about 37 acres), weigh over 10,000 kg (about as much as a blue whale), and be over 1500 years old. And you would have never known it, because it was underground and under bark, and much of it was made up of microscopic threads.

The researchs who discovered the humongous fungus baited for the fungus using poplar sticks, buried under ground, and tested for somatic incompatibility. Basically, if the fungal isolates were genetically distinct, they would repel each other. If they fused, the isolates recognized each other part of the same whole. Comparison of genes further demonstrated that it’s all one big thing. The folks in Michigan are proud of their humongous fungus and celebrate it every year.

But the story doesn’t end there. Later that year, another humungous fungus was claimed near Glenwood, Washington, that was supposed to be 600 hectares, 40 times bigger than the one in the upper peninsula. Though the evidence wasn’t as strong, the question arose. How big can these things get?

In 2003, a paper was published demonstrating an even larger Armillaria clone, in the Blue Mountains of northeastern Oregon. This one was found to be even bigger than the purported thallus of Glenwood, 965 hectares, or 2385 acres. Though the estimates of the age are variable, it's thought that the Oregon Armillaria clone (actually A. ostoyae) could be as old as 8650 years. Can you imagine? An individual organism that might predate the Egyptian pyramids?

Does this seem like deja vu? I just realized that I blogged about this before, and not too long ago. But not as a prestigious Organism of the Day. That part is new. I still think it's one of the coolest stories in mycology. I also think Tom Volk tells the story better, but there it is.

Humungus Fungus Fest

Coming up 12-15 August 2010, the Humungus Fungus Fest in Crystal Falls, Michigan. The festival pays tribute to the Armillaria bulbosa thallus which lives is the area.

Armillaria spp. are basidiomycete, mushroom-forming fungi which feed off living and dead plant roots and stems, decaying them in the process. There are some situations where Armillaria can be an aggressive pathogen, killing even otherwise healthy individuals, but many are weakly pathogenic, opportunistic, or saprobic. The taxonomy of Armillaria has been rather confused, but is being worked out using molecular (DNA-based) tools. Also using these tools, and also through cultural experiments, it has been shown that single genetic individuals (genets) can be found occupying very large areas. The humongous fungus near Crystal Falls is estimated to cover 38 acres, and be at least 1,500 years old, and may be as much as 10,000 years old. The report was published in the prestigious journal, Nature. An excellent and more accessible summary of the article can be found here.

I think this has to rate as one of the top coolest things about fungi. Because this giant living organism is, most of the time, almost totally invisible. Armillaria does produce mushrooms, but only when conditions are right. The body of an Armillaria (or thallus, in mycospeak) is comprised predominantly of microscopically fine threads of mycelium, though these may coalesce and form rhizomorphs, which are sclerotized (toughened) tubes of hyphae that move resources like water and nutrients around the thallus. Dense mycelial fans can also be found under the bark of some affected trees. And most of it is underground, or hidden under bark. Thus, while invisibility comes in being hidden below ground, and also in being microscopic. And in a third sense it is invisible. In being so large that the eye could not see the entire limit of its body from a single vantage point.

However, the fungal record for largest and oldest living thing, being only the first one to surface, did not last. A 600 hectare thallus was identified in Washington state, and an Armillaria ostoyae thallus in the Blue Mountains of eastern Oregon was ascertained to cover 965 hectares, or about 2,385 acres, and could be as old as 8,650 years. As far as I know, this is the current record holder for Armillaria thalli.

I don't know if I'll make it to the festival in Michigan. It does look like a lot of fun. (I will not type "-gi" next to that, I will not. Because that would be totally corny). Cribbage Tournament!

Jack O'Lantern Mushrooms

My eye was drawn to these babies as I was driving around town this afternoon. I do believe what we have here is jack o lantern mushrooms (Omphalotus sp.). They are common at the base of oak trees or on adjacent roots (as these were). These ones were really bright orange, so they stood out and I just had to stop and tiptoe across a bit of lawn to get these pics.
I've had a friend mistake these for chanterelles, as they do have decurrent gills, but fortunately she didn't eat them, as they are poisonous. Probably won't kill you, but you won't be happy for a while if you do try eating them.

Montana!

So, if you've visited my blog from stem to stern, you've seen the map of all the states I've visited. It's only there to shamelessly burnish my own glory, I admit. Well, right now I'm in Montana, which means I've added a state to my life list, leaving only Alaska, Delaware, Missouri, North Dakota, and South Dakota. I may have visited Delaware and not remembered it.

I'm planning on starting a post-doc out here in January, at least part-timing between Montana and Alabama, since I've got some roots in Alabama the Beautiful.

Here's a pic taken in Alabama by a friend of mine. I wish I could've seen this in person. That does appear to be a Hericium (coralloides or ramosum?), which is edible and choice.

Dead Man's Foot

The fungus of the moment is Pisolithus tinctorius, the dead man's foot (or also the "dog turd fungus". It is so named for the shape of the fruiting body, which erupts out of the earth like the start of a zombie invasion.
Actually, this fungus is one of the "good guys", in that it is ectomycorrhizal. Okay, so decaying otherwise recalcitrant matter is not bad, and being a pathogen is bad if you're a pathogen that people want to use is bad from the perspective of the people who are in competition with the pathogen, but mycorrhizal species are considered "good" by most people. Mycorrhizas (alt. mycorrhizae) are considered mutualistic symbioses between fungi and plant roots. Fungi, being fundamentally microorganisms, can explore the soil much better than plant roots, because of their high surface-volume ratio. Thus they can get at nutrients like phosphorus and other elements that plants need from soil better than the plants themselves. In return for their superior soil scavenging services, the fungi get paid in carbon, sugar, photosynthate, which the plants make from carbon dioxide in the air and send down to their roots.
Spores of dead man's foot are commonly sown in with pine seedlings to help them to get established.

Highlights of the root dig

Spent a good part of last week digging roots over in Georgia. My dissertation is a study of the decline of longleaf pine (Pinus palustris) and the role of Leptographium spp. and their insect vectors. What that means is I spend a lot of time collecting small beetles and "rolling" them to find out what fungi they're carrying. And it also means I go out and occasionally dig up some pine roots to see what fungi the insects may have introduced into the trees.

When digging roots, we also collect soil to see if the fungi may be just hanging out in the soil next to the roots (they usually aren't), and a few other things to try and figure out how the trees have been affected by the fungi and insects. This particular root, above, is notably munched up by insects. All those little white bits are where the insects chewed in and pitch came running out.

Another highlight of the root dig was coming upon this critter, a pine snake.
What do pine snakes have to do with fungi? If you'll indulge...
Red Cockaded Woodpeckers are an endangered species. Lots of folks around here hate the little bird because it ties 'em up in lots of "green tape". They are endangered because their preferred habitat is longleaf pine forest, which used to be all over and is now quite rare. This is the only woodpecker, so far as I know, that makes its nesting cavities in live trees. Why make your house in a live tree? Because of these pine snakes, which can climb a pine tree and raid your eggs. The woodpecker pecks holes around the entrance to the cavity to release the resin which acts as a deterrent to the snake. Eww! Sticky snake!
But where do the fungi come in? So the woodpeckers also prefers trees that are infected with Phellinus pini, which is a wood decay fungus causing a disease called red heart, which breaks down some of the cellulose in the wood which makes it easier to excavate. Hey, if you had to dig your house out of a live tree with your face, wouldn't you want the softest tree possible?

Then I had to head back out to the woods on Monday, to collect insects, and I came across this little guy. Not sure, but I think it's a baby cottonmouth. I'll get back to you on that.