A second-year 6-man Dundas flat has made the alarming discovery of a large rubbery mushroom sprouting from their carpet. What is it? Is it delicious or poisonous? Friend or foe? And what does it mean for the state of their flat? Critic Te Ārohi consults a Botany student to find out.
Disclaimer: I am not saying you should eat these. Please don't eat your carpet mushrooms and then say I told you to, or the Botany Department will regret ever teaching me about mushrooms.
Here in Dunedin we are (hopefully) all familiar with the dangers of mould manifesting in our insufficiently ventilated, damp, depressing flats. When some friends sought my help in identifying a mushroom apparently growing in their flat, I was expecting your run of the mill mould – either scary black mould, a classic blue bread mould, or some strange pink shower algae. I couldn’t be further from the truth.
I’m a second-year Botany student with what most of my friends would call a weird obsession with mushrooms. I would call it a fun little hobby. By no means am I an expert, but I have become familiar with a handful of the common fungus seen around Dunedin – familiar enough, at least, to have some idea of what I'm looking at. Combine this with access to University microscopes and a generous amount of Googling, and I have become somewhat proficient at IDing the specimens I find.
My degree from Internet University has led to a lot of questions from my friends, usually the classic: "Is this little brown guy magic?" The answer’s no, unfortunately, and it’ll ruin your kidneys faster than Gordon’s Gin on an empty stomach. More concerning was a friend telling me he’d been suckling on a water bottle with a black-green slime-infested mouthpiece. Spoiler alert: that’s not good, and you shouldn't need a scientist to tell you that.
These aforementioned house mushrooms were definitely my most intriguing – albeit concerning – ID request so far. My friends weren’t kidding. Expressing equal measures of excitement and distress in the hush of the Law Library, I was presented with pictures of full size, fleshy, ear-shaped MUSHROOMS. These things were as big as your store-bought Swiss Browns, though looked more like something you’d cop from Look Sharp for Halloween. While large mushrooms are usually associated with the outdoors, these particular specimens seemed to desire a more comfortable lifestyle, carving out a niche beside the lamp in the carpet of their lounge.
Naturally, the foreign fungus was cause for some worry about the moisture content of their home – but my friends had more pressing questions. Firstly, posed Jono, "What is it?" Eva followed this with, "We need some more mushrooms for the pizza! Is it edible?” I am all for foraging (groceries ain't cheap) and you can find a surprising amount of tasty mushies here in Ōtepoti. But this fleshy cup looked either like a part of your body or something you’d insert inside – and every girl knows that just because you boil a Diva cup, that doesn’t make it edible (or safe).
The next hopeful recreational use for their unexpected guest was also thwarted. Considering its lack of blue hue and gills characteristic of the third, much beloved category of psychedelic shrooms, they didn’t fit the bill for these either. Off the bat, I was fairly certain it would come under the genus Peziza (not pizza), which are commonly known as cup fungi.
As with many fungi, it is difficult to ID species level from a photo alone. Thus, a day or two later I crept into the dark, damp, Dundas abode, and plucked the offending specimen from the carpet. Sporelock Holmes, if you will. The living room was seemingly invaded by the sprawling limbs of clothes horses spread with damp washing. I’m not one to judge – but I am one to deduce, and the question of how the living room became moist enough to support such large mycological life was becoming clearer. It was spore galore.
Off to the lab I went, clutching my creepy and veiny prize. There, I sliced and diced the specimen, gave it a long hard stare, and then uploaded it on iNaturalist for the real experts to identify. A quick image search and some previous knowledge gave me the genus. I then made a cross section revealing ascospores pretty consistent with the size and shape of Peziza varia, backed up by some distinctive cells in the middle of the fruit. Squinting at the shroom the way you would a pair of marginally clean socks, I gave it ye olde sniff test. Lo and behold, it was odourless like most Peziza. My personal oracle Jerry Cooper confirmed my observation on iNat.
Peziza varia is a saprotrophic fungi, meaning it eats organic material. It’s an introduced species that, when not terrorising students, can be found infecting soil, wood, and wood chips. This could be very scary, and potentially pretty disastrous, as many saprotrophic fungi actively dissolve and decay wood. However, studies on Peziza domiciliana, another mushroom that likes to grow inside, have shown that they are often happy to just suck up nutrients from the carpet without actually risking any structural integrity of the house. Cross your fingers for this variety if you’re sporting spores indoors.
The reason mould is such a concern is due to the spores. Peziza varia spores have thankfully not been found to cause any health issues but it does have an asexual form called Chromelosporium. Mould is a loosely defined term without scientific meaning, but the fluffy asexual spores produced by Chromelosporium would fit this description. These have a greater likelihood of causing allergic reactions or lung lesions – bad news for the asthma kids out there. Safe to say, I’m really hoping that this is not happening in my dear friend's home.
Short of tearing up the carpet, the only really solid treatment would be removing the moisture. Mycelial networks are hardy and unphased by any attack on their fruiting bodies. Plus, even if you can't see the mushrooms, the twining roots (hyphae) are probably still there. In my professional opinion, this is as good a reason as any for a big apology and the gift of a dehumidifier or two from the landlord.
So what have we learned? Treat carpet-bound Peziza varia like your backyard grass: not quite toxic and technically edible, but you wouldn’t use it like a veggie patch for pizza toppings. Maybe as a last resort when all of your student loan has already gone to Speight’s Summit Ultras. Best paired with homemade gone-off-milk-turned-cheese for a real treat. Personally, I’ll be sticking to the button mushrooms safely supplied by Big Supermarket.