Straw mushrooms or paddy straw mushrooms, Volvariella volvaceae, are a tropical mushroom grown, as the name suggests, in straw, most abundantly in Southeast Asia. Attempts to cultivate them in North America have been unsuccessful. I have only seen fresh straw mushrooms for sale in Toronto once or twice; more usually, you'll find them canned.
Straw mushrooms are usually harvested when young, when they are fairly small, perhaps an inch or 2 long, and tan in colour. At this stage they are oval in shape, and in fact are said to be in their "egg stage"; as they age, the caps will erupt, resulting in a more common mushroom shape. There's a photo of them at both stages at
Straw mushrooms can be stir fried, but are more usually used in soup, particularly tom yam or tom kha gai. Very tasty and delicate, if you can get them fresh. I'd say, if all you can get are canned, substitute oyster mushrooms, or good old button mushrooms.