Piggyback Rosegill

Piggyback Rosegill (Volvariella surrecta) is one of the most remarkable agarics in temperate woodland because of where it grows: not on wood, litter or soil, but directly on the ageing fruit bodies of another mushroom, almost always the Clouded Funnel, Clitocybe nebularis. Small clusters of slim white caps rise from the collapsing grey host like a colony on a raft.

Structurally it is a typical rosegill. The genus Volvariella, in the family Pluteaceae, is defined by free gills, a pink to salmon spore print and a persistent sac-like volva at the base of the stem, with no ring. Volvariella is essentially Pluteus with a volva — and V. surrecta is the fungicolous specialist of the group.

Because it depends entirely on finding a suitable host, the species is local and unpredictable, appearing in some autumns and not others even where Clouded Funnel is abundant. Its epithet surrecta means "risen up", describing the way the small caps stand erect from the decaying host beneath.

Cap

The cap is 2–5 cm across, at first ovoid or conical-campanulate and expanding to convex or broadly bell-shaped, sometimes with a low umbo. It is white to pale greyish-cream, dry, and covered with fine silky radial fibrils that give a satiny sheen; the centre may be faintly greyish. The margin is often slightly inrolled at first and can be minutely fringed.

Gills

The gills are free from the stipe, crowded, fairly broad and ventricose, white at first and turning a clear salmon-pink or flesh-pink as the spores mature. The transition is often rapid once the cap expands.

Stipe

The stipe is 3–7 cm tall and 3–8 mm thick, cylindrical, tapering slightly upwards, white and silky-fibrillose. At the base is a membranous, sac-like volva — a loose white to greyish cup enclosing the stem base, usually free from the substrate and easy to see when the fruit body is lifted. There is no ring.

Flesh and spore print

The flesh is white, thin and soft, and does not change colour when cut. The spore print is pink to salmon-pink; spores are smooth and ellipsoid. The host tissue immediately beneath the cluster is usually a soft, greyish, decaying mass in which the individual host cap can still be traced.

This species fruits on the decaying fruit bodies of other agarics, overwhelmingly the Clouded Funnel (Clitocybe nebularis), and occasionally on other large Clitocybe and related species. It therefore occurs wherever its host does: in leaf litter of deciduous and mixed woodland, often in rings or troops under beech, oak and conifers, and sometimes in hedgerows and shrubby parkland.

The season is autumn, following the host's own fruiting, so it appears typically from late September to November when the Clouded Funnel caps begin to soften and grey. It is found across temperate Europe and is recorded from North America and Asia, but everywhere it is patchy and considered an uncommon find, appearing in localised outbreaks rather than year after year at the same spot.

Volvariella surrecta is fungicolous — it lives on and consumes another fungus. Its mycelium invades the tissue of the host fruit body and, in some cases, the host mycelium in the litter beneath, drawing nutrients from it and converting the collapsing cap into a platform for its own reproduction. In this respect it is best described as parasitic or, on already senescing hosts, as a specialised saprotroph of fungal tissue.

Because the resource is small and short-lived, the fungus must complete its cycle quickly: spores land on or near a suitable host, colonise it as it matures and softens, and produce fruit bodies within days. Host colonies that have persisted for several seasons in the same litter appear more likely to be affected, which is why outbreaks tend to recur in particular woods.

The habit of growing out of another mushroom is diagnostic, but other rosegills should be compared. Silky Rosegill (Volvariella bombycina) is much larger, with a shaggy silky-hairy white or yellowish cap and a big brownish volva, and it grows from wounds and hollows on standing hardwood trunks, especially elm and maple. Stubble Rosegill (Volvopluteus gloiocephalus) is large with a smooth, distinctly viscid grey to grey-brown cap and grows from soil, compost and disturbed ground.

White Amanita species also have a volva but differ in having a ring on the stem, gills that are adnexed or narrowly attached, and a white spore print rather than pink. Pluteus species share the free gills and pink spore print but have no volva at all and grow on wood.

Another fungus-on-fungus association to compare is the Powdery Piggyback (Asterophora lycoperdoides), which grows on blackened Russula caps but is small, brown, powdery-capped and has thick, distant, attached gills.