Big Sheath Mushroom

Appearance

The cap of "Volvopluteus gloiocephalus" is between 5 and 15 cm in diameter, more or less ovate or conical when young, then expands to convex or flat, sometimes with a slight central depression in old specimens. The surface is markedly viscid in fresh basidiocarps; the color ranges from pure white to grey or greyish brown. The gills are crowded, free from the stipe, ventricose, and up to 2 cm broad; they are white when young but turn pink with age. The stipe is 8–22.5 cm long and 0.7–1.5 cm wide, cylindrical, broadening towards the base; the surface is white, smooth or slightly pruinose. The volva is 2–3 cm high, sacciform, white and has a smooth surface. The flesh is white on stipe and cap and it does not change when bruised or exposed to air. Smell and taste vary from indistinct to raphanoid or similar to raw peeled potatoes. The spore print is pinkish brown.

The basidiospores are ellipsoid and measure 12–16 by 8–9.5 µm. Basidia are 20–35 by 7–15 µm and usually four-spored, but sometimes two-spored basidia can occur. Pleurocystidia are 60–90 by 20–50 µm with variable morphology: club-shaped, fusiform, ovoid, and sometimes with a small apical papilla. Cheilocystidia are 55–100 by 15–40 µm with similar morphology to the pleurocystidia; they completely cover the gill edge. The cap cuticle is an ixocutis. Stipitipellis is a cutis. Caulocystidia are sometimes present, measuring 70–180 by 10–25 µm; they are mostly cylindrical. Clamp connections are absent from the hyphae.

Naming

Molecular analyses of the internal transcribed spacer region clearly separate the four species currently recognized in "Volvopluteus", but morphological identification can be more difficult due to the sometimes overlapping morphological variation among the species. Size of the fruit bodies, color of the cap, spore size, presence or absence of cystidia and morphology of the cystidia are the most important characters for morphological species delimitation in the genus. "V. earlei" has smaller fruit bodies in diameter), has no pleurocystidia, and the cheilocystidia usually have a very long apical excrescence. In "V. asiaticus" the majority of the pleurocystidia have an apical excrescence up to 10–15 µm long and the cheilocystidia are predominantly lageniform. "V. michiganensis" has smaller basidiospores, on average less than 12.5 µm long. "Volvariella acystidiata", known from central Africa and Italy, somewhat resembles "Volvopluteus gloiocephalus". It can be distinguished from the latter by its smaller fruit bodies, with caps up to 3 cm in diameter, and, microscopically, by the complete absence of cheilo- and pleurocystidia.

Distribution

This species has been reported from all continents except Antarctica, usually under names such as "Volvariella gloiocephala" or "Volvariella speciosa". Molecular data have so far corroborated its occurrence in Europe and North America but records from other continents remain unconfirmed.

Habitat

"Volvopluteus gloicephalus" is a saprotrophic mushroom that grows on the ground in gardens, grassy fields, both in and outside forest areas, and on accumulations of vegetable matter like compost or woodchips piles. It has also been reported fruiting in greenhouses. In China, it grows in bamboo thickets. It usually fruits in groups of several basidiocarps but it can also be found growing solitary. It is not unusual for a season of "spectacular" fruiting to be followed by several years with no appearance of the mushroom.