There are many varieties of these wonderful mushrooms, said to have been produced for more than 1000 years in southern China. Black or brown, they add a particular flavour and aroma to Chinese dishes. The very large ones, with a lighter colour and a highly cracked surface, are the best and so are usually the more expensive. They can be bought in boxes or plastic bags from Chinese grocers and are fairly pricey, but a little does go a long way. Keep stored in an airtight jar in a cool, dry place.