Cellar Cup

The Cellar Cup is a pale, thick-fleshed Peziza whose species epithet cerea — waxy — describes the slightly translucent, softly waxen look of its tissue. It is one of a small group of pezizas that have adapted to man-made mineral substrates, which is why it turns up far more often in cellars, boiler rooms, greenhouses and building sites than it does in undisturbed woodland.

In form it is a fairly straightforward cup: a rounded bowl that expands with age, sometimes becoming irregular or lopsided where it is squeezed against a wall or pipe. The colour is muted — cream, buff, pale ochre or dull yellow-tan — and it lacks any bright pigment, hairs or obvious stalk.

Because it fruits in sheltered indoor and semi-indoor spaces, the Cellar Cup can appear at almost any time of year when moisture is available, unlike the strictly seasonal woodland cup fungi. It is often noticed only when a colony erupts across damp plaster or in the gravel of a greenhouse bench.

Fruiting body

The cup is typically 2–8 cm across, occasionally larger, starting as a nearly closed ball and opening into a deep bowl, then a shallow saucer. The margin stays fairly even at first and becomes slightly wavy or torn with age. Crowded specimens fuse and distort one another.

Surfaces

The inner surface is smooth and pale ochre, cream-buff or dull yellow-tan, sometimes with a faint pinkish or greyish cast in age. The outer surface is paler, whitish, and covered in a fine granular or mealy bloom that can rub away.

Stipe

Absent or reduced to a narrow point of attachment; the cup usually sits directly on the substrate, sometimes half-buried in sand or mortar dust.

Flesh & spore print

The flesh is comparatively thick for the size of the cup, whitish to pale buff, soft and waxy in texture but still brittle, breaking cleanly. There is no latex and no colour change on cutting. The spore print is white, and the spores are smooth and elliptical.

This species is strongly associated with lime-rich and man-made mineral substrates: damp mortar and plaster, cement, brick dust, sand, gravel, and soil heavily mixed with builders' rubble. Classic sites are cellar floors and walls, disused boiler rooms, greenhouse benches, the gravel under raised beds, and the shaded ground beside building foundations. It will also fruit outdoors on bare compacted paths and disturbed calcareous soil.

Indoors, where moisture and temperature are buffered, fruiting can occur through much of the year; outdoors it follows the usual spring-to-autumn pattern after wet spells. It is widely distributed in temperate Europe and North America, and its distribution tracks human construction more than any natural vegetation type.

The Cellar Cup is saprophytic, living on scattered organic matter — decayed wood fragments, paper, plant debris and organic binders — mixed into damp mineral material. It does not attack sound masonry itself; the mycelium exploits the thin organic film and cellulose fragments held in the moisture of the substrate, so its presence is really an indicator of persistent dampness.

As an operculate ascomycete it produces its spores in asci arranged in a layer across the inner face of the cup. Ripe cups discharge spores in synchronised puffs when disturbed by air movement, an efficient way of reaching new damp surfaces in the still air of an enclosed room.

The closest confusion is with the Domicile Cup Fungus (Peziza domiciliana), which shares the indoor, mineral-substrate habit but is generally whiter and thinner-fleshed, often develops a more irregular, contorted shape, and has noticeably larger spores under the microscope. The Palamino Cup (Peziza repanda) is larger, warmer tan, distinctly thin-fleshed, and grows on wood, mulch and sawdust rather than mortar.

Peziza varia in the broad sense covers several look-alikes of similar pale brown colour that fruit on wood and wood-rich soil; substrate is the practical field separator. Any similar cup with violet tones on burnt ground is more likely the Violet Fairy Cup (Peziza violacea), and any that releases a yellowing juice from cut flesh belongs to the Peziza succosa group.