Category Archives: Fungi

Ghosts rise from forest duff

2015-07-13 indian pipe monotropa 018Ghost plant, Monotropa uniflora, is now flowering in shaded woodlands. The species is also known as Indian pipe or corpse plant. Each stem is about finger-high and has a nodding flower at its tip. The plant’s pallor tells the story of its peculiar feeding methods. Rather than using pigments to gather sunlight, the roots are sheathed with fungi from whom the plant gets its food. Monotropa is quite specialized, connecting to a small number of Russula fungi species. The fungi in turn feed themselves by tapping the roots of trees, so Monotropa is indirectly feeding from other plants, using a fungus as the money-laundering intermediary. Whether the fungus gets anything in return from Monotropa is not known. The plant is usually regarded as wholly parasitic.

2015-07-13 indian pipe monotropa 009Monotropa belongs to the Ericaceae plant family, a group that includes heathers, blueberries, rhododendron, and sourwood. These species often live on nutrient-poor acid soil where symbiotic relationships with fungi help the plants to thrive in conditions that are otherwise hostile to roots. Monotropa also favors acidic areas and is often found in deep shade under conifers. It seems that Monotropa took its family heritage and changed it from mutualism to piracy. If so, this is the genus that no-one likes to discuss at the Ericaceae family reunion. Quite why the fungus would put up with its parasite is a mystery. It could be that the evolution of defensive mechanisms has not happened because the tiny Monotropa plant draws so little food compared to the supply that the fungus receives from trees. It is perhaps no coincidence that nearly all non-parasitic Ericaceae plants are shrubs and trees, and only Monotropa is a tiny sprout. The plant’s narrow range of fungal associates may also indicate that only a few fungus species can be fooled. All this has conservation implications: Chris Martine and Alison Hale have recently published a fascinating article suggesting that chemicals from invasive plants such as garlic mustard may disrupt the relationships between Monotropa and its fungi, causing population declines.

The species lives in North America, Asia, and Central America, with large geographic gaps between each population. Recent studies of DNA show that these populations have diverged from one another and have distinctive genetic signatures, suggesting that they might best be regarded as different species. How the species came to have such a distribution is unknown: the dust-like, winged seeds may have traveled by wind or the distribution may be an echo of the ancient geographic connections among these continents.

Five days after the bloom pictured above, pollinating bumblebees have done their work and the red fruit capsules are swelling. The flower’s rain-shedding, bee-welcoming droop has straightened and the fruit points directly to the sky, presumably the better to catch some favorable winds to a neighboring uncolonized fungus, or to Japan.

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Hidden communities of fungi nestled within tree leaves

A maple leaf is more than it appears to be. Its substance is made not just from plant cells, but from a community of many species. “Maple” is in fact part plant, part fungus, part bacteria. Just as the human body is comprised of a vast “microbiome,” plants are also composite creatures.

To get a glimpse at this diversity, I cultured some of the fungal species found on and within the maple leaves growing on the tree by the front door.

To look at the fungi on the leaves’ surfaces, I dabbed maple leaves onto pertri dishes containing agar and fungus food, then waited a few days. Here is one such dish, displaying the diversity of species found on the leaf. Of course, many fungi don’t like petri dishes, so what we see below is a mere fraction of what is actually present on the leaf. The leaf itself is not so thickly coated; the petri dish gives fungi a place to grow and reveal themselves to our eyes.

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These fungi from the surface are a mixed bag. Some are potentially harmful to the leaf and will ultimately eat the leaf away when it drops in the autumn. Others are likely protective or live as commensal squatters. Some feed on the droppings of caterpillars or the honeydew of aphids. A few might have drifted from the humans, goats, and stacked firewood below.

To peek at fungi that live inside the leaf, “endophytes,” I sliced some leaves into tiny pieces, sterilized their surfaces, then placed them onto petri dishes. Compared to the leaf “prints” taken from the surface, it took a couple of days longer for these endophytic fungi to appear on the dishes, but they too showed quite a diversity of forms. Here are two examples:

Maple_endoMaple_endo2To make sure that I was not simply growing fungi that were wafting in the air or present on my forceps, I also ran some “control” plates which yielded either nothing at all or a few white blobs.

How endophytic fungi interact with tree leaves is largely unknown. But one of their roles is protective, secreting substances that deter the growth of pathogenic fungi. For example, endophytes isolated from Douglas maple release a chemical that poisons a variety of nasty plant diseases.

Interestingly, endophytes in sugar maple leavs seem to be more diverse in old growth forests than they are in younger, managed forests, or in urban areas. But these are preliminary findings. We have only the haziest understanding of the ecology of the fungal world hidden within leaf laminae.

Inside each leaf: a whole community. Within the community: hundreds of stories waiting to be heard. One story is clear, though: if we believe that creatures — humans included — live apart from “the other,” we’re deluded.

Fog happens, and the woods rise into it.

The overlook at Green’s View offered an interesting prospect this morning. The hundred mile view was shortened by the enveloping cloud to less than one hundred feet.

fogThe fog penetrated the forest, hazing and graying views through the trees.

fog2The smell was deliciously tenebrous, seeping into the dim air from the darkness of the soil. Shrews and moles must inhale the same rich earthiness as they burrow.

Although we imagine springtime coming from elsewhere, a warm breeze blowing birds and warmth from the tropics, in reality most of the year’s new life rises from the musty earth, surging through layers of decay.

The first significant signs of this life have now appeared in Shakerag Hollow. Harbinger-of-spring (also called salt-and-pepper plant, Erigenia bulbosa, a carrot relative with an edible tuber) has raised hundreds of tiny blooms over the mountainside, each one standing barely taller than the upper surface of the leaf litter.

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harbinger of springFungi are also poking through, spreading their spores from colored cups.

cup1cuo2And the animal world is alive. Hairy woodpeckers call, perhaps starting their  breeding season. Orange centipedes lumber across the litter, seeking prey into which to sink their poisoned fangs. Spiders, although withdrawn in their hiding places, have their presence revealed by the foggy air. Every web is a bright cloud of droplets. In some places, funnel-web spiders had strewn the forest floor with dozens of newly constructed traps.

funnelLeaves of toothwort, spring beauty, bloodroot and trillium were unfurling, but their flowers were not yet emerged. Soon, though, the smouldering wet soil will blaze.

Shelf fungus as a rain shelter for woodpeckers?

Older black locust trees in our region are often rotten on the inside. Fungi worm through the tree trunks, digesting their cores. When these fungi are mature enough to reproduce, they sends filaments (hyphae) to break through the tree bark. The exposed hyphae grow into “shelves” on the trees’ trunks. These shelves are comprised of the remains of thick-walled dead hyphae, intermingled with thin-walled living strands. The “wooden” feel of the shelves comes from the walls of the dead cells; the spores are made by living hyphae. “Wooden” is not quite accurate: fungi cell walls are strengthened not with the stuff of wood, cellulose, but with chitin, a molecule that also finds use in the exoskeletons of insects. The shelves are tough enough to persist for many years.

Rotten trees provide habitat for many animals. Much of this utility is mediated through the work of woodpeckers. In excavating a fresh nesting hole each year, woodpeckers leave a trail of convenient roosting and nesting sites for other species, most obviously many bird species (titmice, chickadees, great-crested flycatchers, wood ducks, owls, etc), some mammals (flying squirrels), and bees (feral honey bees love big hollow trees). Most woodpeckers will only attack trees that are partly rotten, so it is the combination of bird and fungus that produces this real estate boon in the forest.

Woodpeckers and fungi may also have more short-lived associations. My friend Joseph Bordley pointed out to me that the tree bark under shelf fungi is often scratched up. This seems to be particularly true for shelves of Phellinus robiniae on locust trees. I found one such example this weekend on the trail to Bridal Veils falls near Sewanee. As the photos below demonstrate, the distressed bark sits directly below the shelf. Are woodpeckers using shelves as shelters in the rain? Despite keeping my eye on locust trees for many years now, I’ve yet to see any birds under shelves in rain or shine. I’d be interested to hear whether anyone has any other relevant observations. Might animals be gnawing the wood to slurp mushroom spores? Is there some other reason for the mysterious scratchings?

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Fifty Shades of Grey: Woodland Edition

Sitting in the woods with my class last week, I was struck by how grays had come to dominate. The light environment is transformed. Of course, a “fifty shades” wisecrack had to work its way into my impromptu lesson on the visual aesthetics of the forest. The witticism turned into a small project for my walks of the last week: pay attention and find these shades. So here they are, fifty photographs of variations on the theme.

Gray is the most egalitarian of hues. Indeed, its essence is that is not a single color. Instead, gray gives us a muted echo of all the light spectrum, a moody version of white. Contrast this with the bias of other pigments — reds, blues, yellows — that reflect just a tiny slice of the light available to them.

Gray is an unassuming mirror of the world and a quiet companion for its more assertive kin. It absorbs metaphors with ease, having combined light and dark: ash, silver, lead, pepper. A suitable tone, then, for winter reflections.

Happy Solstice, fellow ramblers.

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Pelting rain, then mist, more rain, and…salamanders

Intermittent downpours are not ideal weather for outdoor classes, unless your topic for the day is: salamanders!

So a hardy (and uncomplaining — YSR!) group of cyclists headed out in the rain, destination Shakerag Hollow. This is the first of many days of salamandering for my Advanced Ecology and Biodiversity class. We’ll be documenting the local fauna and comparing communities among streams with varying degrees of sedimentation.

The focal stream for the day yielded many Spotted Dusky Salamanders, Desmognathus conanti. These stocky animals are fast movers: you need quick hands to catch them. They are about five inches long and hide under rocks, emerging at night and in downpours to feed on insects and other small prey.

Spotted Duskies stake out a tiny stretch of stream for their home range, so we made sure to put them back exactly where we found them.

In addition to salamanders, we found several crayfish, including this one, expertly captured and held by my colleague David Johnson, that has two babies attached to the underside of its tail. The females usually carry eggs in this position, but youngsters generally swim off on their own.

The woods were also full of fungi, including this stinkhorn……and a spectacular growth of what I think is “chicken-of-the-woods,” a species that is edible (to some; for others it causes considerable distress). This fungus was visible from about fifty meters away. It glowed through the mist of the forest. No, it burned. But salamander-like, we survived the fire.

Earthstar

Indulge me by letting me start with a short quote from The Forest Unseen:

August 8th — Earthstar. Summer’s heat has coaxed another flush of fungi from the mandala’s core. Orange confetti covers twigs and litter. Striated bracket fungi jut from downed branches. A jellylike orange waxy cap and three types of brown gilled mushroom poke from crevices in the leaf litter. The most arresting member of this death bouquet is the earthstar lodged between rafts of leaves. Its leathery outer coat has peeled back in six segments, each segment folded out like a flower’s petal. At the center of this brown star sits a partly deflated ball with a black orifice at its peak.”

And, several years later, right on cue in early August, here are the earthstars in Shakerag Hollow. They must be the most gorgeous fungi ever. The one pictured above is Geastrum saccatum. It is about the size of a quarter.

My essay in The Forest Unseen rambles off in the direction of golf balls. Here I’ll keep my eye on the fungus.

Earthstars belong to the Gasteromycetes (“stomach fungi”), a motley collection of mushrooms that hold their spores in a stomach-like sac. Other members of the group of puffballs, stinkhorns, and bird’s nest fungi. Unlike the gilled mushrooms, bracket fungi, and others that forcibly eject spores using microscopic catapults, Gasteromycetes take an entirely passive approach to dispersing their spores. They hope for a raindrop, or the step of a beetle, or a prod from a falling twig to puff their spores into the air.

The evolution of these Gasteromycete fungi reveals some interesting evolutionary processes. Once the “stomach-like” form evolves, there is no turning back. Although “normal” gilled mushrooms have evolved earthstar or puffball-like structures at least four times, there are no known evolutionary transitions in the other direction. Why? The catapult mechanism is so complicated that it is very unlikely to re-evolve once it has been lost. After the catapult genes have been discarded, only a very long stretch of time and some lucky mutations could bring them back.

The loss of forcibly discharged spores has unexpected consequences. It turns out that having a passive spore dispersal mechanism makes a species more likely to split into new species. Exactly why this should be so is not clear. Perhaps their spores do not travel as far, so allow populations to become isolated from each other, leading to reduced gene exchange and then speciation? Regardless of the mechanism, the Gasteromycete fungi have been speciating more rapidly than their gilled relatives.

So the future belongs to the earthstars. Especially those that can figure out how to eat golf balls.

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For those interested in digging deeper, the relevant articles in the scientific literature are listed below.

Hibbett, D. S., E. M. Pine, E. Langer, G. Langer, and M. J. Donoghue. 1997. Evolution of gilled mushrooms and puffballs inferred from ribosomal DNA sequences. Proceedings of the National Academy of Sciences, USA 94: 12002–6.

Wilson, A. W., Binder, M. and Hibbett, D. S. (2011), Effects of gasteroid fruiting body morphology on diversification rates in three independent clades of fungi estimated using binary state speciation and extinction analysis. Evolution, 65: 1305–1322. doi: 10.1111/j.1558-5646.2010.01214.x