[Thai straw mushroom, Paddy Straw Mushroom, Volvariella volvacea]
These are grown on rice straw and are not yet widely available fresh even in California. They are, however, available canned in stores catering to Asian communities. Mistaking the almost identical but highly toxic death cap (Amanita phalloides) for straw mushrooms has resulted in death and/or need for liver transplants among Asian immigrants to the US and Australia.
Straw mushrooms are canned in two forms: egg shaped with the cap and stem still completely encapsulated by a shroud called the volva, or partially opened with a conical cap on a short thick stem. These are called "unpeeled" and "peeled" on the can but the "peeled" is just a more mature form of the "unpeeled". The unpeeled can be much larger than the one in the photo. They are also available dried (right in photo) but not so commonly. Straw Mushrooms are very important in Southeast Asian cuisines, particularly Thai. In Vietnam they may be found growing wild on old termite mounds. These are much stronger in flavor than cultivated and fetch a much higher price.
More on Mushrooms.
Buying: These are available in almost all markets serving East Asian and especially Southeast Asian communities. They are commonly packed in 15oz/425gm net weight cans. Drained weight will vary from 7oz/200gm to 8oz/225gm. Recipes should always call for drained weight but sometimes they call out by the can (1 can, 1/2 can). That will always be the 15oz can.
Storing: In an unopened can they will keep for a a couple of years without problems. Once the can is opened put them in a tightly sealed jar in the refrigerator covered with the liquid from the can and they will last a week or so.
Cooking: Straw mushrooms are almost always cooked (and canned ones are already lightly cooked in the canning process). Peeled straw mushrooms are generally used in soups because they're too fragile for stir fries and the like. Unpeeled work fine in stir fries, especially since they're always added right near the end. Canned mushrooms require only momentary cooking to bring them up to temperature. When using the unpeeled they present a more interesting effect if cut in half lengthwise as shown in the photo. If you get them at just the right stage they look like happy alien faces.
Dried straw mushrooms aren't common, but are available in larger Asian markets. They are somewhat different (a little more intense) in flavor, but still recognizable as straw mushrooms. Soak them in hot water for 1/2 hour before cooking with them, and do use the soaking liquid in the recipe, it is quite good.