In mid-October, I went on a guided mushroom hike with the Peterborough Field Naturalists in Mark S. Burnham Provincial Park. The park is a 39 ha old-growth forest (OGF) with trees up to 300+ years old. In 2019, AncientForest.org identified several ancient trees of this unique OGF so close to the town of Peterborough. They documented several trees with diameters (DBH) ranging from 29 cm to 79 cm and ages ranging from 183 years to 334 years. Large old trees included eastern hemlock, white cedar, American basswood, sugar maple and beech. The largest tree was an eastern hemlock, estimated to be 207 years old. Several old sugar maples ranged from 183 years to 334 years old.  

Hike leaders Sue Paradisis and Rachel Baehr (of Trent University) led us through lowland swamp beneath a tall canopy of magnificent old hemlocks (some ranging up to 298 years old), cedars (ranging up to 276 years old), and several old sugar maples (ranging up to 334 years old). Then we scrambled up the drumlin into the autumn colours of a mixed deciduous forest of beech, ash, and maple trees, and an old American basswood (102 years old).

Throughout the walk I was aware of the underground symbiotic mycorrhizal network in the soil that connects an ecosystem’s vegetation and helps transport nutrients and defense compounds from plant to plant.

The Fungal Network

Dario Cortese of The Startup tells us that a single fungus mycelium can spread over 4 square miles (10.5 km²), giving fungi the ability to populate a vast volume of soil, scouting for nutrients and water to transport over long distances. Plants, whose roots don’t extend nearly that far, have used the impressive fungal network for over 400 million years. For millennia, plants have traded their surplus sugar made by photosynthesis in exchange for increased access to water, nutrients and protection from pathogens.

This mutualistic relationship is a win-win scenario between plant and fungus—until the plant grows old and dies. Then the fungus simply eats it—sometimes it’s the same fungus. But even in feeding on the rotting wood, the saprophytic fungus transforms dead organic matter and hard lignin into simple molecules that go back into the soil and provide nutrients that new plants can use—completing Nature’s wise cycle of being.

When a Fungus Changes from Ally to Antagonist

In a previous article, I talked about the endophytic fungus Coprinellus domesticus that inhabited a fallen black walnut tree in the forest by my house. When a tree is alive and healthy, endophytic fungi form a mutual relationship with it, providing protection from pathogens and sharing beneficial secondary metabolites. Endophytic fungi are universally present in every plant species. Rashmi, Kushveer and Sarma in Mycosphere report that “a single tropical leaf may harbour 90 endophytic species.” But, when the tree grows old and starts to die, the relationship changes.

The relationship of the endophytic fungus with its host tree works on a continuum, potentially switching from mutualism to antagonism, depending on environmental pressures. The endophyte may become saprobic once the host starts the senescence process.

In a sudden moment of clarity, I saw how fungi interconnect all things on this planet, living in, on, above and below everything. Fungi literally stitch a living tapestry of balanced tension between symbiosis and antagonism, all orchestrated by the environment and climate. With that realization, I felt very small, but connected and part of something huge and truly awesome.

Fungi of Mark S. Burnham Old Growth Forest

During our several-hour walk through the old-growth forest, we looked for the fruiting bodies of the forest’s fungal network. We found saprobic (decomposing) fungi on the decaying wood of nursery logs and stumps that littered the forest. Examples included several polypores on hemlock snags and logs, Pholiota at the base of a maple, the slime mould Wolf’s Milk gorging on old cedar logs, coral fungi, and frilly Turkey Tail everywhere.

We saw examples of fungal guttation, when mushrooms ‘weep,’ just like leaves do. This is a way the mushroom excretes excess water and is common among corticioid and many bracket fungi such as polypore Fomitopsis pinicola.

The interpretive walk was educational, satisfying and fun. I saw several fungi I had not seen before, including Dog’s Vomit Fungus on an old beech log and the Lacquered Polypore at the base of an old hemlock tree.

But one mushroom in particular caught my attention.

It was just another pretty brown saprobic mushroom growing out of a rotting cedar log in a bed of moss. The mushroom was unassuming but rather beautiful, forming attractive clusters in a mix of moss and porous decaying wood. Their caps were convex to flat and rufous brown at the centre then fading to honey yellow towards the edge. The gills were cream-coloured and furrowed. I noticed that the stems (stipe) were streaked and sported a pale collar or annulus—remnants of the partial veil. Many were bent like the trunks of black locust in a thick forest. At the base of several mushroom stipes, I spotted a white cloud of fungal mycelium, spreading out into the moss.

I only realized after checking my field guide that this ordinary brown mushroom is one of the most deadly on the planet. This little brown mushroom turned out to be Galerina marginata.  

Deadly Galerina marginata

First Nature tells us that Galerina marginata contains the same deadly poisonous toxins that occur in Amanita phaloides, the Death Cap (an unassuming white mushroom) and Destroying Angels (Amanita virosa complex). In a nutshell, the α-amanitin toxin binds to and disables an enzyme responsible for making new proteins. Without the enzyme, cells can’t function, resulting in severe liver derangement and culminating in hemorrhagic liver necrosis. Without prompt treatment, the victim will experience rapid organ failure, coma, and death. Thirty grams or half a cap of Galerina or Amanita is enough to kill a human with onset of symptoms within six to 24 hours.

Also known as Funeral Bell in the UK, Galerina marginata is a saprobic fungus, which likes well-decayed conifer stumps and broadleaf tree logs. It is best seen in autumn and is found all across the northern hemisphere’s temperate zone (including Europe, Asia, and North America). According to First Nature Galerina means ‘like a helmet’ and marginata means bordered, referring to the generally paler marginal area of the cap compared with the centre.

The hygrophanous cap is initially hemispherical then becomes broadly convex or almost flat shaped. The cap, which can be 1-7 cm in diameter, is rufous brown in the centre, fading to honey yellow towards the edge. Margins may be faintly striate. Gills are close, adnate, pale cream-fawn to ochraceous honey-coloured and turn slightly rusty as they mature. The stem, 2-7mm n diameter and 2-7 cm tall, are often curved. Buff at the apex and browner towards the base, they are longidunally fibrillose below the pale ring or collar.

Good friend and naturalist Merridy Cox is fond of telling people that for every edible mushroom there is an evil twin. In this case the evil twin posed by Galerina marginata has its edible twin in the popular edible mushroom, Kuehneropmyces mutabilis (Wood Tuft or Brown Stew Fungus). The Wood Tuft is a close relative and has a similar size and colour range but a pale cap centre and darker rim. Mycologist Timothy J. Baroni cautions mushroom foragers that Galerina marginata can also be mistaken for the edible Honey Mushroom (Armillaria spp.) which occur in similar habitats, have a vaguely similar brownish colouration, but are larger, produce white spores, and have black stiff hairs on the cap.

Little brown mushrooms (LBMs) often go unnoticed because they are heard to spot and are usually too small to consider worth eating. The “Deadly Galerina” is therefore usually not dangerous on its own. Fungus Fact Friday contend that “the real danger from this mushroom comes when it is accidentally collected along with a group of edible mushrooms.” Velvet Foot Mushroom (Flammulina velutipes), Brick Caps (Hypholoma sublateritium), and Magic Mushrooms (Psilocybe spp.) are most commonly confused with G. marginata. All of these can be found on decaying wood.

Fungus Fact Friday suggests “you should never eat any little brown mushrooms growing on wood.” Period. I agree. Not worth the risk.

References:

Barron, George. 2014. “Mushrooms of Ontario and Eastern Canada.” Partners Publishing, Edmonton, AB. 336pp.

Baroni, Timothy J. 2017. “Mushrooms of the Northeastern United States and Eastern Canada.” Timber Press, Inc., Portland, Oregon. 598pp.