These mushrooms, whose name means "pine" (matsu) and "mushroom" (take) grow under pine trees in Japan, parts of China, and the North American West Coast. They're also found in parts of Northern Europe. Sought-after and prized by the Japanese, these mushrooms can sell for up to $2000 per kilogram in Japan. Here in San Francisco, I found them going for $10 per pound. Their seasonal window is very short, usually from October to January.