Mosses are the lowly ones, the soft green carpets of the damp places, the plants that grow where nothing else will. But without mosses, there would be no bogs, no peat, no wetlands as we know them. They are the engineers of the soggy world. And there was once a moss that grew taller than any alive today – a sphagnum that rose 30 centimetres from the water, its stems thick and branching, its leaves large and water-holding. It formed mats so dense that you could walk on them without getting your feet wet. It was the giant swamp moss, and it is gone. Size and water-holding capacity made it special. Sphagnum mosses are remarkable plants – they can hold 20 to 30 times their dry weight in water. They acidify the water around them, preventing decay and allowing peat to accumulate. They are the foundation of the bog. The giant swamp moss was the master of this strategy. Its stems were thick and upright, its leaves were large and cup-shaped, perfect for holding water. It could hold perhaps 50 times its weight in water – a living sponge that kept the wetland wet even in drought. It built the bog. A healthy peat bog is built on the bodies of sphagnum mosses. The moss grows at the surface, while the lower parts die and accumulate as peat. This process takes thousands of years, building a deep layer of carbon-rich soil. The giant swamp moss would have been the primary builder of New Zealand's lowland peat bogs – the engine of the wetland. Its dense mats provided habitat for tiny creatures – springtails, mites, worms, insects. Its water-holding capacity kept the bog wet, which in turn supported a community of specialised plants – sundews, orchids, sedges. Mosses reproduce by spores, released from capsules on slender stalks. The giant swamp moss produced spores in large quantities, but its growth was slow. It spread by fragmentation as well – pieces of the moss breaking off and growing into new plants. That strategy works when the bog is vast and the water is clean. It fails when the bog is drained. Swamp drainage and peat extraction destroyed it. When Europeans arrived, they drained the great lowland wetlands for farming. They dug ditches, laid pipes, burned the peat. The giant swamp moss, which needed permanent waterlogging to survive, could not grow on dry land. Its stems collapsed. Its leaves dried out. Its spores could not germinate. Peat extraction was the final blow. Peat was dug from the bogs for fuel and garden soil. The giant moss, which had taken thousands of years to accumulate, was stripped away in a single season. By the 1910s, it was gone. The last patches were probably drained or dug up by a farmer who had no idea what he was destroying. He drained the bog, planted grass, and the marsh ghost disappeared. The smaller sphagnum mosses survived. They are more adaptable, able to grow in smaller bogs, wet gullies, and regenerating wetlands. They are the survivors, the low-growing ones, the mosses that kept their heads down. But the giant swamp moss is extinct. A few pressed specimens in a herbarium, a few spores in a core sample, and the memory of a moss that used to build the bogs. We drained its world. Then we wondered why the bog felt so dry.