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| Earth on May 12, 2008

Have you seen mushrooms growing in circles?

Certain kinds of mushroom spores sprout a tangle of tube-like threads, which spread out horizontally in all directions – like spokes radiating from the hub of a wheel.

If you’ve ever seen mushrooms growing in circular pattern, you’ve seen a “fairy ring” – from the old belief that fairies danced inside the circle of mushrooms.

Only a few kinds of mushrooms form fairy rings. You might have seen the mushroom called the Giant Puffball. Mushrooms are a type of fungus, and fairy rings form as a result of the way certain types of fungi grow.

These fungi start growing underground from a single spore. The spore sprouts a tangle of tube-like threads, which spread out horizontally in all directions – like spokes radiating from the hub of a wheel. That’s what gives rise to the circular pattern. The part of the fungus you see – the mushrooms – springs up at the edge of the circle.

Scientists can measure the advance of a fungus from the increasing size of a fairy ring – so they can figure out when the ring started to grow. Some fairy rings have been found that may have been growing for four hundred years.