Big fungi have little fungi upon their backs to mine them, and little fungi have lesser fungi, and so ad infinitum… (Adapted from Augustus DeMorgan)

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Back in school, I learned that fungi play diverse and important roles in ecosystems, helping to break down organic matter and recycle nutrients, often through symbiotic relationships with plants and other organisms (e.g. lichens). Fungi act variously as decomposers and nutrient cyclers, as mutualists, and sometimes as pathogens.

Saprophytic Decomposers: Most fungi are saprophytic decomposers, breaking down dead plant and animal matter, returning essential nutrients to the soil. This process is crucial for nutrient cycling and supporting plant growth and all life. Most mushrooms we see in the forest and elsewhere are decomposers.

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Mutualists: Some fungi are mutualists, forming symbiotic relationships with plants and animals, where both organisms benefit. For example, mycorrhizal fungi form a symbiotic relationship with plant roots, helping plants absorb water and nutrients, while the fungi receive carbohydrates from the plants. The underground symbiotic mycorrhizal network in the soil connects an ecosystem’s vegetation and helps transport nutrients and defense compounds from plant to plant.

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Another example are the lichens, which are an association of fungi, algae and bacteria that work together to form a kind of community-organism, each putting in something for the group and ultimately the ecosystem. Lichens are more appropriately called a micro-ecosystem, an association of symbiotic organisms working together and living more successfully for the association. Lichen inhabit most substrates, from trees and the ground, to rocks and artificial surfaces, to tiny leaves, and even the air.

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Parasitic Pathogen: Fungal pathogens are natural components of healthy forest ecosystems, playing a significant role in eliminating weak and unfit trees. These fungi feed on living hosts, and don’t necessarily kill them. An example is the cedar-apple rust caused by the parasitic fungus Gymnosporangium juniperi-virginianae. This fungus needs two hosts to complete its life cycle, living as a parasite on the largely unaffected juniper host, where it forms galls from which its spores hop onto a nearby apple tree to infect them.

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Shapeshifting Fungi

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Many fungi are shapeshifters, shifting from one role to another, depending on the changing conditions. The Firerug Inkcap mushroom (Coprinellus domesticus) is an endophytic fungus that forms a mutualistic relationship with a host tree, providing protection from pathogens and sharing beneficial secondary metabolites. When the tree grows old and dies, the fungus shifts from a mutualistic to antagonistic role as a saprophyte, helping the tree decompose and returning nutrients back to the soil.

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The Brittle Cinder Fungus (Kretzschmaria deusta) often starts as a pathogen, entering a live tree and eating away at the living tissue of the tree, then changing to a saprophytic decomposer when the tree dies, breaking down the dead materials and returning them in accessible form to the environment.

We all know that fungi play an important role in decomposing dead organic matter into available nutrients for the continuation of life on Earth. But what about fungi that grow on other fungi? What’s that all about?

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Fungi Growing on Other Fungi

True to the rhyme above, fungi often grow on other fungi, preferring their own kind to other substrates like wood, bark, soil, etc. The relationship is often a parasitic or decomposing one. Most of these relationships are a form of negative or positive symbiosis encompassing three types of relationship of fungi with other fungi:

• Mycoparasitism: one fungus parasitizes another fungus, consuming it partially or wholly for nutrients. Trichoderma secretes enzymes that break down the cell walls of the host fungus, then absorb its nutrients. The fungus Escovopsis physically attacks and degrades the hyphae (thread-like structures) of another fungus it feeds on. In the case below, the fungus may feed on the flesh of another mushroom cap.
• Mutualism: a cooperative relationship where both fungi benefit. I wasn’t able to find an example of mutualism between fungi; however, there are many examples of fungal mutualism with other organisms such as mycorrhiza (beneficial symbiosis between fungi and tree roots) and lichen (beneficial symbiosis between fungi and algae or cyanobacteria). In some fungus-growing insects, the insects cultivate and farm fungi for food, and in return, the fungi receive protection and a stable environment to grow. A non-symbiotic example of mutualism occurs when mammals eat fungi and help disperse its spores.
• Mycodecomposition: a saprophytic fungus grows on the dying or dead body of an old fungus, in which the saprophyte uses the organic material of the mushroom carcass as a substrate to grow on. Collybia grows on dead mushrooms, consuming them as they decompose. Older boletes succumb to Hypomyces chrysospermus, which help them decay and release their nutrients back into the environment.

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Mycoparasitism: Mycena & the Bonnet Mold

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During late fall in Watershed Park, I saw many tiny mycena mushrooms growing everywhere: on the leaf-covered ground, and on moss-covered logs and stumps. One, the tiny and beautiful Bleeding Bonnet (Mycena sanguinolenta) was, in turn, colonized by another fungus, Bonnet Mold (Spinellus fusiger), a pin mold that parasitizes many genera of Mycena. The parasite grows inside the mushroom, without killing it, but taking nutrients from the flesh and releasing hair-like structures out of the Mycena cap like a bad hairdo. Spinellus’s dark, round sporangia at the ends of its filaments contain spores that eventually disperse, looking for another mushroom to live on and eat.

I’d seen this parasitic fungus before; a few years ago in Ontario’s Trent forest, I found it growing on another Mycena. When it’s infected, Mycologist Tom Volk describes it as a “punk rock Mycena,” with aerial filaments spreading out ending in dark pin-head-like spores.

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Mycoparasitism: White Coral Fungus & Helminthosphaeria clavariarum

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Spreading their creamy-coloured fruiting bodies on the step moss-covered ground near Douglas fir trees, with which they form a mycorrhizal relationship, were many colonies of White Coral mushroom (Clavulina coralloides). Also called Wrinkled Coral fungus or Crested Coral fungus, these delicately beautiful creamy white branching mushrooms are actually quite tiny, reaching about 2 cm high, and typically found in moist, shaded areas during late summer and fall, often under conifers or hardwoods.

As I mentioned, Clavulina coralloides is ectomycorrhizal, forming a symbiotic and beneficial relationship with the roots of conifer trees—in this case Douglas firs—and exchanging nutrients with them.

I noticed that some of the fungi were turning blue-grey from the base up. This, I later found, is caused by the parasitic ascomycete fungus Helminthosphaeria clavariarum, which spreads from the base up, presumably drawing nutrients from the host. The parasitic fungus doesn’t seem to affect the coral fungus much, except its appearance. One source mentioned that H. clavariarum can cause more sparse and abnormal branching in the host fungus.

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Mycodecomposition: Zeller’s Bolete & Bolete Eater Mold

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By late November, many of the Zeller’s Boletes (Xerocomellus zelleri) in the Douglas fir forest of Watershed Park, BC, were covered in a white mold, Bolete Eater Mold (Hypomyces chrysospermus), which, as the name implies, primarily attacks the fruiting bodies of boletes, especially in their final stages of decay.

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Fungi interconnect all things on this planet. Helping others fully live; helping them efficiently die. Fungi literally stitch a living tapestry of balanced tension between symbiosis and antagonism, all orchestrated by the environment and climate–and completing a cycle that has marched on for millennia. And will likely continue for many more in the future.

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