Yellow-juice Cup

The Yellow-juice Cup is the best-known member of a small group of pezizas whose flesh exudes a juice that oxidises to a vivid yellow. Outwardly it is a plain fungus — a modest grey-brown to drab ochre-brown bowl sitting on bare damp earth — but a single cut across the margin makes it unmistakable as the released liquid stains the tissue, the blade and the fingers a clear sulphur yellow.

It belongs to Peziza in the family Pezizaceae and shares that genus's brittle fleshy texture, absent stalk and smooth inner spore surface. The species epithet succosa means juicy, referring directly to the watery exudate.

Because its plain colouring gives few other clues, this is one of the cup fungi where the chemistry of the flesh, rather than the shape or colour of the fruiting body, is the primary field character. Field guides routinely instruct observers to nick the margin as the first identification step.

Fruiting body

Cups are 2–6 cm across, deeply bowl-shaped when young with an incurved margin, expanding to a shallower saucer that may split or become slightly wavy. They are often partly sunk in the soil surface.

Surfaces

The inner surface is smooth and dull: greyish brown, pale olive-brown or drab ochre, sometimes with a faint lilac or fawn tinge. The outer surface is paler, whitish-grey to buff, and finely scurfy or minutely granular.

Stipe

Absent or reduced to a short buried base; the cup sits directly on damp soil.

Flesh & spore print

This is the decisive feature. The flesh is whitish and brittle, and when cut or broken it releases a watery juice that turns bright yellow within seconds, staining both the cut surface and anything it touches. The spore print is white; the spores are elliptical and coarsely warted, usually with two conspicuous oil droplets.

The Yellow-juice Cup grows on bare or sparsely vegetated damp soil, particularly heavy clay, in deciduous and mixed woodland. Classic sites are shaded path edges, ditch sides, eroded banks, the churned ground of old track ruts, and the exposed soil around uprooted trees. It prefers moist, loamy or calcareous ground and avoids deep undisturbed litter.

Fruiting occurs from early summer through autumn, following periods of steady rain, often in scattered groups of a few to a dozen cups. The species is widespread across temperate Europe and North America and is reasonably common wherever there is shaded bare woodland clay.

It is saprophytic, drawing its nutrition from fine organic matter and decaying root and litter fragments distributed through the upper soil. Its preference for disturbed and eroded ground suggests it competes best where the mycelia of litter-dominating fungi have been stripped away, giving it open substrate to colonise.

As with other operculate ascomycetes, the inner surface of the cup is a dense layer of asci that fire mature spores upward into moving air. The yellowing exudate is a product of oxidation of compounds stored in the flesh and appears reliably in fresh material, fading in old or dried specimens.

Peziza michelii is the closest relative and also yellows when cut, but its inner surface carries a distinct purplish or lilac-brown flush and its flesh is thinner. Peziza succosella is smaller with a paler cup and differently ornamented spores. Both require a careful colour comparison rather than a habitat one, since all three share bare woodland soil.

The Common Brown Cup (Peziza phyllogena) shares the soil habitat and general size but is a much darker olive to chocolate brown inside and its cut flesh does not yellow at all. Pale, wood-inhabiting species such as the Palamino Cup (Peziza repanda) are tan, thinner-fleshed, unchanging when cut, and grow on wood chips or rotting stumps rather than clay.