The oyster mushroom – that broad-capped, pale-gilled fungus that grows on dead wood in clusters, looking like a shelf of oysters on a fallen log – is one of the most cultivated mushrooms in the world. But there was once an oyster mushroom that grew where no oyster mushroom grows today – in the mangrove forests of northern New Zealand, on the rotting roots and submerged timber of the saltwater edge. Its caps were larger than a dinner plate. Its flesh could survive the salt and the tide. It was the giant mangrove mushroom, and it is gone. Size and salt tolerance made it special. A 25-centimetre mushroom is a spectacular thing – a broad, pale cap, sometimes with a hint of grey or brown, rising from the dark mud of the mangrove forest. Its gills were white or pale cream, crowded and forked. Its stem was tough and fibrous, anchoring it to the submerged wood. It grew in clusters – sometimes five, ten, twenty caps together – a pale garden on the rotting mangrove roots. It decomposed the mangrove. Mangroves are tough trees – their wood is dense, waterlogged, resistant to rot. The giant mangrove mushroom was one of the few fungi that could break it down. Its mycelium penetrated the dead wood, secreting enzymes that digested the tough fibres. It turned fallen branches and dead roots into nutrients, releasing them back into the estuarine ecosystem. Its caps provided habitat for small insects and crustaceans. Its spores were carried by the wind and the tide, spreading through the mangrove forest. It reproduced by spores, released from the gills beneath its cap. The spores were tiny, easily carried by the wind. When they landed on suitable dead wood – preferably mangrove – they germinated, sending out thread-like hyphae that colonised the timber. That strategy works when the mangrove forest is vast and the dead wood is abundant. It fails when the mangroves are cleared and the estuaries are filled. Mangrove clearance and land reclamation destroyed it. When Europeans arrived, they cleared the mangrove forests for farmland, housing, and harbour development. They drained the estuaries, filled the mudflats, built seawalls and roads. The giant mangrove mushroom, which needed decaying mangrove wood to grow, lost its habitat. The remaining mangroves were fragmented, their dead wood removed or burned. Without a steady supply of rotting timber, the fungus could not survive. By the 1910s, it was gone. The last specimens were probably collected by a naturalist who had no idea he was holding the final individual. He pressed them, dried them, put them in a drawer. And the estuary fell silent. The smaller oyster mushrooms survived in other parts of the world. Pleurotus ostreatus still grows on dead wood in forests and gardens – smaller, less salt-tolerant, but alive. But New Zealand's giant mangrove mushroom is extinct – a ghost of the estuary, a pale cap that no longer rises from the mud. We cleared its forest. Then we wondered why the estuary felt so empty.