Cedar Cup Identification Guide

The Setting and the First Impression

The Cedar Cup is a fungus you find by choosing the right tree rather than the right wood. Stand under a mature cedar in a park, an old churchyard, an arboretum, a cemetery or a planted avenue, somewhere with a big deodar, Atlas or Lebanon cedar whose lower branches sweep the ground. Then look at the bare, compacted soil beneath the canopy, especially where the fallen needle litter is thin and the ground has been kept clear by shade and drip.

What you are looking for barely reads as a mushroom. The usual first sighting is what appears to be a small torn hole in the soil surface, or a crumpled brown paper bag pushed halfway out of the ground, with soil crumbs and cedar needles clinging to it. Only when you crouch and see the pale interior facing the sky does it resolve into a cup.

Once your eye is trained, a colony often turns up in a loose arc or scatter across several square metres, sometimes with a dozen fruit bodies at different stages: closed knobs still buried, half-emerged split domes, and fully open stars.

Reading the Cup

The fruit body begins life underground as a closed, subglobose to egg-shaped body. As it expands it pushes up against the soil crust and the upper part splits radially into five to twelve irregular, pointed, tooth-like lobes that curve back and outwards. That stellate rupture is the defining architecture, and it explains why a specimen looks so ragged and asymmetrical.

The open cup measures 3-8 cm across, occasionally to 10 cm, and remains deep: the buried lower half is a substantial bowl, sometimes as deep as it is wide, which is easy to miss if you snap the specimen off at ground level.

The inner surface, the hymenium, is smooth and matt, coloured pale grey-cream, whitish or a soft ochre-buff, sometimes with faint wrinkling towards the base and often a little darker as the specimen ages. The outer surface is a complete contrast: brown to dark brown and densely covered in coarse hairs, so it feels felty and slightly harsh to the touch, and soil grains and needle fragments are permanently bound into it.

Under a hand lens the exterior hairs are visible as stiff, brown, pointed bristles. In a water mount they resolve into thick-walled, septate hairs, tapered to a point and often slightly wavy, which is a good confirmation of the genus.

Base, Flesh and Colour Change

There is no stipe. The fruit body is sessile and attached at the bottom of the bowl by a mass of soil-bound hyphae, which is why careless collecting simply tears the base off.

Excavate properly. Push a knife into the soil ten centimetres out from the cup, undercut it, and lift the whole block, then wash it later. A specimen removed this way retains its true depth and its stellate lobes, and it is impossible to make sense of the species from a flat brown rosette picked off the top.

The flesh is 2-3 mm thick, pale ochre-brown, brittle and slightly waxy-crumbly. It snaps rather than tears when bent. There is no latex and no strong odour, and cutting produces no colour change, though the hymenium may darken slightly where it has been handled or bruised.

Getting a Spore Deposit

This is an operculate ascomycete, so the spores are shot upwards from asci lining the inner surface rather than dropped from gills. A print is still obtainable and worth taking.

Set the cup with its hymenium facing downwards, propped a few millimetres above a glass slide or a piece of dark card, inside a closed container with a little moisture, and leave it for several hours. A faint whitish bloom of spores accumulates below. A more theatrical field test on a ripe specimen is to breathe warmly on the open hymenium: a visible puff of spores may be released all at once, a phenomenon common to many large cup fungi.

Under a microscope the spores are large and distinctive, colourless, smooth-walled and broadly ellipsoid, roughly 25-35 by 14-18 micrometres, and each typically contains one large oil drop or two smaller ones. The asci hold eight spores, open by a hinged lid rather than a pore, and their tips do not turn blue in iodine. The paraphyses are slender and only slightly swollen at their tips. Spore size alone will separate this species from most of its relatives.

Substrate, Season and Association

The Cedar Cup is very tightly linked to Cedrus. It is recorded almost exclusively under planted deodar, Atlas and Lebanon cedars, and the relationship is thought to be mycorrhizal or at least closely host-dependent rather than a matter of simple litter decay. Practically, that means the fastest way to find it is to survey cedars rather than to survey soil.

It is semi-hypogeous by habit, developing entirely below the surface and only emerging at maturity, which is why it can be abundant at a site for years without anyone noticing.

The season is late winter to spring, typically February to May and sometimes from January in mild wet weather, well before the main autumn fungal season. It is widely recorded across Europe including Britain and Ireland, and in other regions where ornamental cedars have been widely planted. Sites are faithful: a cedar that produced cups one spring will very often produce them again.

Separating the Look-alikes on Morphology

Geopora arenicola and G. arenosa are the closest relatives. They are much smaller, generally 1-3 cm across, they grow in sandy or disturbed soil, on dune slacks, path edges and bare banks rather than under cedars, they typically fruit later in the year, and their spores are appreciably smaller. Size, habitat and season taken together separate them comfortably.

Geopora foliacea and other members of the genus overlap in general appearance and are best separated on spore dimensions and hair structure, so measure rather than guess.

Humaria hemisphaerica is superficially similar in that it is a brown-haired cup with a pale interior, but it sits entirely on the surface of soil or rotten wood in deciduous woodland, it is smaller at 1-3 cm, its interior is a clean whitish to greyish-white, and its brown bristles project prominently from the margin like eyelashes. Its spores are ornamented with warts and carry two oil drops. It is also a summer to autumn species.

Sarcosphaera coronaria is the most impressive mimic of the growth habit, because it too develops underground and bursts stellately through the soil. It is larger, up to 15 cm, its exterior is whitish to pale cream rather than brown and hairy, and above all its inner surface is a striking lilac to violet-grey. It grows in calcareous soil under beech and conifers, mainly in late spring.

Peziza species share the general cup form but sit on the surface, have smooth or merely scurfy exteriors rather than dense brown bristles, retain a more regular circular outline, and rarely split into radiating lobes.

Tarzetta cupularis and T. catinus have a distinctly toothed or crenate margin and a short stalk, but their surfaces are whitish-buff and finely scurfy rather than densely brown-hairy.

One last false lead: a scrape or dig made by a bird or mammal under a cedar can leave a star-shaped depression in the litter that looks convincing at ten paces. The presence of a pale hymenium and a felty brown hairy exterior settles it immediately.

Working Checklist

Under a mature cedar, late winter to spring; a deep cup 3-8 cm across, developing buried and bursting through the soil with five to twelve reflexed pointed lobes; pale grey-cream to ochre-buff smooth interior; dark brown, densely bristly exterior with adhering soil; no stipe; brittle pale ochre flesh with no colour change; large smooth ellipsoid spores 25-35 by 14-18 micrometres with one or two oil drops.