Oyster Mushroom Powder Capsules (Pleurotus ostreatus) 100% pure powder, no fillers 30 count 200 mg. each About Oyster Mushrooms As is true with all fungi, oyster mushrooms can usually be found growing on dead or decaying wood. The most active growing seasons for oyster mushrooms are in spring and fall. The caps of these mushrooms are large, capable of growing up to 10 inches in diameter. The caps are shaped like fans, or, as the name implies, oysters. When the oyster mushroom is young the cap is flat, but as it ages the cap turns up. These mushrooms are colorful, and can be found in white, yellow brown, tan and pink or a combination of these colors.