Japan is one of the leading producers of shiitake mushrooms. These mushrooms are notoriously difficult to cultivate on a commercial scale — especially when using the 1,000-year-old Japanese technique of growing them on logs. In the US, indoor-grown shiitakes sell for upwards of $8 a pound, while forest-grown shiitakes have commanded a much higher price, up to $18 a pound. The most premium shiitake mushrooms are called white flower shiitake, and the forest-grown versions can sell for over $160 a pound. White flower shiitakes have noticeable white cracks on the caps and a strong flavor, but even just a few drops of rain can ruin them. Here's why forest-grown shiitake mushrooms are so expensive.