The golden oyster mushroom (Pleurotus citrinopileatus) is a close cousin of the grey oyster I dissected above. Instead of grey, it has a neon yellow cap, and it is prolific. The fungus itself mainly grows on dead or dying hardwood trees, breaking down the tough wood fibres. Golden oysters are "gilled mushrooms", and a single gilled mushroom can release up to billions of spores. Oyster mushrooms also happen to be one of the few carnivorous mushrooms – preying mercilessly on nematode worms.

It is invisible for most of the year, living as mycelium, fungal strands within the wood. But beginning in spring, it sends out its fruiting body – what we would recognise as the mushroom itself. Huge yellow clusters cascade out of logs and trees, each mushroom itself producing millions of microscopic airborne spores.

Native to Asia, the fungus was brought over to the US to be cultivated for food sometime around the early 2000s. Because it fruits so heavily, it proved to be popular with both professional and home growers. It has a high yield, meaning more profit for growers.

The mushroom is now found across the world. It's spreading in Switzerland, and has been found in Italy, Hungary, Serbia and Germany. There are reports of the golden oyster growing in the south of the UK too. The Royal Horticultural society has issued advice warning people against growing non-native species, especially the golden oyster, saying it was "highly invasive" and capable of causing "severe damage" to local fungal communities.

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"We found that trees colonised by golden oyster have, on average, about half the fungal biodiversity as trees without the golden oyster. And so that was a huge indicator that they're likely out competing the native fungi that were there," says Veerabahu.

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Other invasive species meanwhile are appearing in Europe. In October 2025, Poland's national forest management body sounded the alarm after a North American species, the slender golden bolete (Aureoboletus projectellus) was found in the Unesco-protected Białowieża Forest.

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Climate change is also believed to be changing the distribution of fungi across the world. One species, the strikingly orange "ping pong bat fungus" (Favolaschia calocera), originally hails from tropical Madagascar. But it's been showing up in the wild in Dorset, southern England, where its effects on native fungi are unknown, something scientists believe is being helped by rising global temperatures.