Blistered Cup

The Blistered Cup is one of the largest and most familiar members of Peziza, a big genus of stalkless soil and litter cup fungi in the family Pezizaceae. It is a fungus of rich, disturbed, nitrogen-loaded substrates rather than of natural woodland, and it appears wherever people pile manure, straw or compost.

Its common and scientific names both refer to the same feature: as the cup expands, the inner spore-bearing surface develops rounded swellings and bubble-like blisters, so that the interior looks puckered and inflated rather than smooth. Few other large cups do this so obviously.

It is also notably robust for a Peziza. The walls are thick and firm, the margin stays curved inward long after the cup has expanded, and crowded specimens push against each other and distort into angular, lopsided shapes as they compete for space on the heap.

Cup

Deeply cup-shaped to bowl-shaped, 2-8 cm across and occasionally larger, with a thick wall and a persistently inrolled margin that only slowly unfurls. Crowded specimens grow in overlapping tiers and become compressed, angular and irregular.

Inner (fertile) surface

Pale ochre, yellowish brown, buff or tan, smooth at first and then developing conspicuous rounded blisters, swellings and shallow wrinkles across the surface - the character behind the name.

Outer surface

Paler still, whitish to pale buff, and distinctly scurfy, mealy or minutely granular, sometimes almost warty toward the base.

Base, flesh and spore print

There is no stalk; the cup narrows to a small attachment point, sometimes with white mycelial threads binding straw or compost fragments. The flesh is thick, pale and brittle, snapping cleanly, with no colour change on cutting. The spore deposit is whitish, and the spores are smooth and ellipsoid without oil droplets.

This is a species of enriched, disturbed substrates: manure heaps, well-rotted straw, stable bedding, compost piles, mushroom beds, greenhouse borders, mulched flower beds and heavily manured garden and farm soil. It rarely appears in undisturbed woodland.

Because its preferred substrates generate their own warmth and stay moist, it can fruit at almost any time of year, with the heaviest flushes in spring and autumn. It commonly appears in dense clustered troops, sometimes carpeting a compost surface. The species is cosmopolitan, following agriculture and horticulture across temperate regions worldwide.

Peziza vesiculosa is saprotrophic and strongly nitrophilous, thriving on substrates rich in nitrogen from manure and decomposing straw. Its mycelium colonises the fibrous, partly decayed plant matter of heaps and beds, breaking down cellulose and contributing to the later stages of composting.

It is an early and opportunistic coloniser of freshly turned or newly spread material, capable of producing large fruiting flushes within weeks when moisture and warmth are right. The upward-facing cups discharge ascospores in visible puffs when jarred, and because the substrate is often handled and moved by people and livestock, spores are readily spread to new heaps and beds.

Peziza repanda grows on rotting wood, woodchip and sawdust, has a thinner wall, a smoother inner surface without blisters, and a margin that flattens and becomes wavy rather than staying inrolled. Peziza cerea is paler and waxier, often turning up on damp mortar, brickwork and soil near buildings, again without the blistered interior.

Peziza badia is a much darker reddish- to olive-brown fungus of bare woodland soil and path banks. Peziza varia is thinner-fleshed and grows on wood and wood-rich debris. Among the dung fungi, Ascobolus species are far smaller and speckled with dark protruding asci, and Peziza fimeti is smaller and duller with a less blistered surface.