Never eat a wild mushroom identified only from a website, a book or an app. Have every find checked in person by an expert, such as a mycological society.
Identification
The paddy straw mushroom is usually seen at the button or egg stage: an oval body 2–5 cm long, grey to dark brown at the top, completely wrapped in a whitish universal veil. When the veil breaks, a grey to grey-brown cap opens to 5–15 cm, finely streaked with darker fibres. The gills are free from the stem and change from white to pink as the spores mature. The smooth white stem has no ring, and a large sac-like volva remains at the base. The spore print is pink to salmon.
The combination of volva, no ring, free gills and pink spores distinguishes Volvariella from Amanita, which has white spores and usually a ring.
Habitat and ecology
Volvariella volvacea is a saprotroph of decaying plant material in warm, humid climates. In tropical and subtropical Asia it appears on heaps of rice straw and other agricultural waste after harvest. It needs high temperatures to fruit and does not occur in the wild in cool temperate Europe, where other Volvariella species, such as V. gloiocephala on rich soil and V. bombycina on wood, are found instead.
Uses and importance
Paddy straw mushrooms are a staple of Chinese, Thai, Vietnamese and other Southeast Asian cuisines. The firm, mild-flavoured buttons are added whole to stir-fries, curries and soups such as tom yum. Outside Asia they are mostly sold canned or dried, because fresh mushrooms spoil within a day or two. The species is also of interest as a way to turn crop residues, such as rice straw and cotton waste, into food.
Cultivation
Paddy straw mushroom is one of the fastest cultivated mushrooms: crops can be harvested within about two weeks of spawning. Traditional growers use beds or bundles of soaked rice straw, while modern farms use pasteurised mixtures of straw, cotton waste and other residues indoors. It needs warmth: spawn run at roughly 30–35 °C and fruiting at about 28–32 °C with high humidity. It is sensitive to cold, which damages the mycelium and the harvested mushrooms. Buttons must be picked before the volva breaks, often several times a day.
Safety and edibility
Cultivated paddy straw mushrooms are a safe edible when cooked. The danger lies in picking wild mushrooms that look similar: young death caps (Amanita phalloides) and destroying angels (Amanita virosa) also start as egg-shaped buttons in a volva. Serious and fatal poisonings have occurred when people used to eating straw mushrooms in Asia picked young death caps elsewhere. Never eat wild egg-stage mushrooms on the basis of appearance; identification must be confirmed in person by an expert, such as a mycological society or trained mushroom adviser. Amatoxin symptoms start only 6–24 hours after the meal; seek emergency help immediately if a death cap may have been eaten, even before symptoms.
If you suspect mushroom poisoning, call your local emergency number or poison centre straight away, even before any symptoms appear, and keep the remains of the mushrooms.
Look-alikes
Amanita phalloides (death cap) and Amanita virosa (destroying angel) have white gills and a white spore print, and usually a ring on the stem once the cap opens. Their buttons, cut lengthwise, show the outline of the developing white gills and stem, often with a greenish or white cap. Paddy straw buttons, by contrast, mature to pink gills and a pink spore print and never have a ring. Do not rely on any single feature; buttons are especially hard to identify.
Around the world
Worldwide, paddy straw mushroom is mainly a crop of China, Southeast Asia and India, where it fits well into rice-farming systems. In Europe, North America and Australia it is known mostly as a canned or dried import and from poisoning warnings about confusion with death caps.
