The tasty Japanese seaweed nori is ubiquitous today, but that wasn’t always true. Nori was once called “lucky grass” because every year’s harvest was entirely dependent on luck. Then, during World War II, luck ran out. No nori would grow off the coast of Japan, and farmers were distraught. But a major scientific discovery on the other side of the planet revealed something unexpected about the humble plant and turned an unpredictable crop into a steady and plentiful food source.

Nori is most familiar to us when it’s wrapped around sushi. It looks less familiar when floating in the sea, but for centuries, farmers in Japan, China, and Korea knew it by sight. Every year, they would plant bamboo poles strung with nets in the coastal seabed and wait for nori to build up on them.

At first it would look like thin filaments. Then, with luck, it grew into healthy, harvestable plants with long, green leaves. The farmers never saw seeds or seedlings, so no one could cultivate it. The filaments simply appeared every year. That is, they appeared until after World War II, when pollution, industrialization along the coast, and a series of violent typhoons led to a disastrous drop in harvests. By 1951, nori production in Japan had been all but wiped out.