Silky sheath

Appearance

The fruit body begins developing in a thin, egg-like sac. This ruptures and the stem expands quickly, leaving the sac at the base of the stem as a volva. The cap, which can attain a diameter of up to 20 cm , is white to slightly yellowish and covered with silky hairs. On the underside of the cap are closely spaced gills, free from attachment to the stem, and initially white before turning pink as the spores mature. The mushroom grows singly or in clusters, often appearing in old knotholes and wounds in elms and maples. ''V. bombycina'' contains compounds with antibacterial properties.

The fruit bodies of ''Volvariella bombycina'' are initially egg-shaped when still enclosed in the universal veil. As they expand, the caps later becoming bell-shaped or convex, and finally nearly flattened in age, attaining a diameter of 5–20 cm . The dry cap surface is covered with silky threads. Its color is white to yellowish, becoming more pale approaching the margin. The flesh is thin, soft, and white, and has an odor, resembling raw potatoes. Gills are crowded close together, free from attachment to the stem, and initially white before turning pinkish as the spores mature. The stem measures 6–20 cm long by 1–3 cm thick, and is typically tapered upward or thickened below. It is white, with a smooth surface, and is often slightly curved. The universal veil is membranous, often areolate or scaly, and forms a long, saclike volva that wraps around the base of the stem. It is white to yellowish or dingy brown, and often divided into lobes.

The variety ''V. bombycina'' var. ''flaviceps'' is distinguished from the main form by its smaller, bright yellow caps, up to 3.5 cm in diameter, and its dirty-white, scaly volva. Murrill also noted that it developed a "peculiar sickening odor during drying". ''V. bombycina'' var. ''microspora'' has smaller spores , a yellow cap, and a blotched brown volva. ''V. bombycina'' var. ''palmicola'' also has a yellow cap and small spores , but can be distinguished from the previous varieties by its distantly spaced gills.

Mushrooms produce a spore print with a color ranging from pinkish to salmon. Spores are elliptical, smooth, and measure 6.5–10 by 4.5–6.5 μm. The basidia are club-shaped, four-spored, and measure 19–43 by 6–11 μm. Pleurocystidia are usually spindle shaped, but have a widely variable morphology; they are abundant in the hymenium, and have dimensions of 26–122 by 8–57 μm. The cheilocystidia are similar in morphology and abundance, some may feature knobs held at the end of slender projections up to 20 μm long; dimensions are in the range of 26 and 144 μm long by 8–46 μm wide. Clamp connections are absent from the hyphae of ''V. bombycina''.

The fruit bodies can be readily grown in laboratory culture.

Naming

The combination of a silky white cap, white stem, pink gills, pink spore print, and growth on wood is characteristic of this species and make identification of ''Volvariella bombycina'' in the field relatively easy. Some ''Pluteus'' species have a general similar appearance, and also produce pinkish to pinkish-brown spore prints, but they lack a volva. ''Amanita'' species grow on the ground and make white spore prints. ''V. pusilla'' has a small cap measuring 0.5–3 cm in diameter with silky fibers and short lines visible at the cap edge when moist; it grows in soil in gardens and greenhouses and on lawns. ''V. hypopithys'' has a medium-size white cap that is 2–5 cm in diameter with silky to scaly fibers and lacks the short lines at the cap edge when moist; it grows on the ground in woods. ''V. caesiotincta'' has a bluish-gray cap, while ''V. gloiocephala'' can be distinguished from ''V. bombycina'' by its smooth cap that is sticky when damp, and a white volva.

Distribution

''Volvariella bombycina'' is a saprobic species. Fruit bodies grow singly or in small groups on trunks and decayed stumps of dead hardwoods. Favored species include sugar maple, red maple, silver maple, magnolia, mango, beech, oak, and elm. It is often found in clefts and knotholes of dead or living tree trunks. It has been noted to fruit in the same location for several years. Despite its preference for hardwoods, it has been reported growing on rare instances on coniferous wood. An uncommon species with a wide distribution, it has been reported from Asia , the Caribbean , Australia, Europe, North America, and South America. It acquired protected status in Hungary in 2005, making it a legal offense to pick it. Variety ''microspora'' is known from Venezuela, while ''V. bombycina'' var. ''palmicola'' occurs in the DR Congo.