Peziza ammophila - Dune Cup

Taxonomy

Class: Pezizomycetes

Order: Pezizales

Family: Pezizaceae

Cup fungi, and brown ones in particular, are particularly difficult to identify with certainty; however, the Dune Cup is distinctive not merely because of its growing habitat but also because of the way it develops. A globose fruitbody grows beneath the sand, breaking the surface when fully developed; then the peridium splits into between five and ten pointed petals, which peel backwards to expose the inner surface of the cup. At this stage the Dune Cup looks like an earthstar that has lost its central spore sac. The fertile surface is inside the cup, as with all Peziza species. (The first time I saw one of these strange fungi I assumed that it was the empty dried-up case of an earthball, but there was no sign of any of the spore mass inside and yet clearly it was not a particularly old fruitbody.)

As dry sand blows across the dunes, specks inevitably fall into the cup and trigger the discharge of ripe spores; these are then carried away on the breeze – quite a cunning system for releasing spores at times ideal for their long-range distribution!

Identification guide

Description	2 to 4cm across and 1.5 to 3cm tall; globose at first, opening into a crown-like form as several pointed star-like rays fold back to reveal the inner surface of the cup. Outer and inner surfaces are various shades of ochre or brown. Sometimes the fruitbody is seated on a pseudostipe consisting of sand grains bound together by mycelium, but more often there is no stem.
Spore print	White.
Odour/taste	Not distinctive. Like nearly all of the cup fungi, this species in inedible.
Habitat	The Dune Cup is a saprophyte and, as the specific epithet implies, it is usually found with Marram Grass, Ammophila arenaria.
Season	June to November.
Occurrence	Infrequent.
Similar species	There are at least 100 Peziza species and most are various shades of fawn or brown. Definite identification is rarely possible without microscopic examination, but the distinctive crown-like form and marram grass habitat make the Dune Cup a notable exception.