Comment: Mushrooms have been in the news – again for the wrong reasons. A year after a famous Australian mushroom poisoning court case, there has been an outbreak of mushroom poisonings in California.
These both involve the same mushroom species – the ‘death cap’ (Amanita phalloides). And we have cause for concern here, too: with the autumn mushroom season coming on strong, death caps are out-and-about.
The death cap is responsible for most serious mushroom poisonings in New Zealand, with a pattern echoing the US experience: collection by immigrants unaware of the dangers.
In our case, most poisonings involve immigrants from Asia who collect what they think is the paddy straw mushroom – a death cap lookalike. Asia doesn’t have the death cap, so it isn’t a familiar risk.
Eating mushrooms without knowing exactly what they are is a form of Russian roulette. However, stories of mushroom poisoning give mushrooms a fear factor that is not fully warranted. There are very few deadly poisonous mushrooms and it’s perfectly safe to touch even those – just don’t eat them. And, as a biologist, I find much about mushrooms to marvel at.
Mushrooms are essentially ‘flowers’ – reproductive structures not of plants, but of certain fungi. Their job is to disperse fungal spores. The actual fungus, or ‘mushroom individual’, lives hidden away in the soil or wherever the mushroom is poking out of. It consists of candyfloss-like cells that spread out into a giant network.
This giant cell network is key to how mushroom individuals go about their lives. We usually think of fungi (and hence mushrooms) as decomposers, and many mushroom species are.
‘Fairy ring’ mushrooms, for example, actually encompass several different species. They are found in grassy places, where you’ll often notice them as a ring of darker, thicker grass that the mushrooms appear from. The ring is the outside edge of the cell network, revealing the surprising size of the (constantly growing) mushroom individual.
Some mushroom species decompose wood, thus appearing on dead or dying trees, or growing among wood chips. Their cell networks burrow into the wood, breaking it down. A common example (in supermarkets and parks) is the wood ear (Auricularia cornea). This brown ear-like mushroom, widely eaten in Asian cuisine, is found on dead trees and around 150 years ago was an important export for us to China.
Surprisingly, though, a large number of mushroom species, including the death cap, aren’t decomposers, but are symbionts that live in close partnerships with trees. These partnerships are important and a core part of my plant symbiosis lectures at the University of Auckland is dedicated to them.
In these partnerships, some of the fungal cell network coats tree roots, while the rest pokes into nooks and crannies in the soil. Because they are much finer than roots, these cells access nutrients the roots cannot. They pass these nutrients to the tree in exchange for sugars the tree makes. Thus, this is a true partnership where both benefit – technically speaking, a ‘mutualism’.
The partnership, though, is often more extensive. This is because the network of cells from a single mushroom individual can coat the roots of multiple different trees to form a giant fungus-tree network. A native non-photosynthetic orchid, commonly known as the hidden spiderorchid or icky, even gets nutrients by parasitising these networks, using the mushroom individual as an intermediary to ‘steal’ sugars from connected trees.
Even more diverse than their lifestyles are the forms mushrooms take. Some are tall, others short. Some are large, others small. Some are ornate, others simple. Some come in clusters, others are solitary. Some have little pores rather than gills.
Their shapes range from parasol-like to penis-like, from cup-like to coral-like, and from a ball of spines to just a ball. And to top it all off, they come in a kaleidoscope of colours. Why? We don’t know – it’s a key part of their mystery.
New Zealand has both native and introduced species. The death cap is introduced, typically forming partnerships with the roots of oaks. Another introduced species is the classic red-with-white spots mushroom frequently depicted in fairytales (Amanita muscaria). It is related to death caps, also forming partnerships with the roots of trees. However, it is much less fussy than the death cap, and has invaded deep into our native forests to form partnerships with native tree species that probably displace native mushrooms.
Our native mushrooms don’t usually end up in the news for poisoning people, but are extraordinary in other ways. If you smell a certain ‘aroma’ in autumn around wood chips, it mightn’t be the fault of a negligent dog-owner, but instead a native mushroom that looks like a bright red sea-anemone – the anemone stinkhorn (Aseroe rubra). They smell like dog poo because they want to attract flies to spread their spores.
A similarly extraordinary but less pungent native species is the basket fungus (Ileodicytyon cibarium), which looks nothing like a mushroom but instead like white lattice geodesic balls.
As poisonous, stinky agents of decay and fairytales, mushrooms don’t have it easy getting public love. But they live in a world of colour, diversity and mystery with vast underground networks that recycle organic matter and support the wellbeing of trees. Over the coming months, that world is right outside your doorstep – patiently waiting for alert eyes to discover its wonder.
