Vinegar Cup

The Vinegar Cup takes its scientific name from acetabulum, the Latin word for a small vinegar bowl, an apt description of its deep, goblet-like shape. It belongs to Helvella in the family Helvellaceae, but unlike the saddle-shaped members of the genus it keeps a cup form throughout its life.

What makes it instantly recognisable is the rib system. Thick, pale, rounded ribs rise from the short stout stalk, branch repeatedly, and continue up the outside of the cup well past the halfway point, sometimes reaching almost to the rim. This gives the outer wall a ribbed, cabbage-leaf-like sculpture found in no ordinary cup fungus.

It is one of the more substantial spring ascomycetes of temperate woodland and, because of its bulk and its preference for open path edges, it is among the easier spring cups to spot.

Cup

The fruiting body is a deep bowl or goblet 2-8 cm wide and up to 4 cm tall, at first almost closed and later opening with a wavy, sometimes split or torn margin. It is thick-walled and firm, not papery.

Inner (fertile) surface

Smooth and matt, dark brown, chestnut, olive-brown or greyish brown, usually the darkest part of the fungus and often darkening with age.

Outer surface and ribs

Much paler - whitish, cream or pale grey-brown - and finely downy or minutely mealy. Prominent rounded ribs run from the base upward, forking and rejoining as they climb, and typically extend more than halfway up the outside of the cup.

Stipe and flesh

The stalk is short, stout and whitish, 1-3 cm tall, deeply grooved and sometimes almost buried in the soil so that the cup appears to sit on a ribbed pedestal. The flesh is thick, whitish and brittle, with no colour change on cutting. The spore print is white, and spores are smooth, ellipsoid and single-guttulate.

The Vinegar Cup grows on soil, showing a marked preference for calcareous or lime-rich ground. It appears in broadleaf and mixed woodland, along woodland rides and path edges, on grassy banks, in scrub and in open parkland, often where the ground is compacted or thinly vegetated.

Fruiting is concentrated in spring and early summer, making it one of the season's characteristic large cups. It is widespread across temperate Europe and occurs in North America and temperate Asia. Frequent tree associates include beech, oak, hazel and other broadleaf species, though it also turns up under conifers on suitable soils.

Helvella acetabulum is understood to be ectomycorrhizal, forming nutrient-exchanging associations with the fine roots of nearby trees. Its recurring appearance in the same lime-rich woodland verges year after year reflects a persistent mycelium tied to established host root systems.

The deep bowl orientation is an effective spore-launching structure: mature asci lining the inner surface discharge ascospores upward out of the cup, where air currents carry them away. Spring fruiting takes advantage of soil that is still holding winter moisture but has begun to warm, a window this species exploits alongside other spring ascomycetes.

Helvella leucomelaena is the closest relative in appearance: it is also a deep dark cup with a pale exterior, but its ribs are short and confined to the base rather than climbing the cup wall, and it grows with conifers on sandy or calcareous ground. Helvella queletii has a longer, more distinct grooved stalk with ribs that stop at the junction with the cup.

Large Peziza species such as Peziza varia and Peziza badia are broadly similar in colour but have no ribs at all, sit directly on the substrate without a stalk, and have thinner, more brittle walls. Sarcosphaera coronaria begins as a buried hollow ball and splits open into a star-like crown with a pale lilac inner surface, quite unlike the ribbed brown goblet of the Vinegar Cup.