Hairy Rubber Cup Identification Guide

The setting and the first glance

Late spring or summer, damp deciduous woodland, and you are stepping over a tangle of fallen sticks and small branches on a shaded slope or a stream bank. Something dark catches your eye on a partly buried branch: a cluster of small, dark, top-shaped cups, each looking as though it has been moulded out of black rubber and then filled with a disc of warm reddish-brown. The colour contrast between the near-black outside and the tan to reddish inner face is the first impression, and it is a good one — few things in the woods look like this.

They are usually gregarious. One branch often carries five, ten or twenty fruitbodies in a line along its length, sometimes fused in small clumps where several arose together, and neighbouring branches from the same fall may also be occupied. Old fruitbodies persist for weeks and become blacker, drier and more distorted, but the rubbery feel stays.

Shape and size

The fruitbody is a deep cup to a broad goblet, one to four centimetres across the mouth and about as deep, narrowing below into a short thick stalk-like base a few millimetres to a centimetre long. Young fruitbodies are almost closed, like small dark knobs with a puckered opening; they expand into an open bowl with a rim that is often inrolled at first and later becomes wavy, lobed or split. In dense clusters the cups deform each other into irregular, one-sided shapes.

The outer surface

Run a thumb over the outside. It is dry and dull, dark brown to nearly black, and densely covered in short stiff hairs that give a matted, felted, coarse-suede texture. Under a hand lens the hairs are thick-walled, dark and blunt, forming a tangled tomentum rather than a smooth skin. The hairs continue down onto the stalk-like base, which is usually the most heavily coated part. That black hairy exterior, on a fungus that also feels rubbery, is the pairing to remember.

The inner disc

The upper, inner face of the cup is the fertile surface, and it looks nothing like the outside: smooth, matt to slightly waxy, and coloured reddish-brown, orange-brown, tan or cinnamon depending on age and moisture. Fresh, well-hydrated discs are noticeably warm-toned; drying material darkens towards dull brown. The surface may become slightly veined or undulating in larger fruitbodies but it is never wrinkled into brain-like folds and never black.

The texture test

This is the character that names the species and the one to lead with. Take a fruitbody between finger and thumb and squeeze: it compresses and springs back like a pencil eraser or a piece of firm rubber. Then cut it in half from rim to base with a sharp blade. The flesh is thick — often two to five millimetres and more in the base — gelatinous to rubbery-cartilaginous, translucent and slightly amber to greyish in section, with a firmer, darker outer zone beneath the hairs. It does not snap, crumble or shatter; it yields to the knife and bends rather than breaking. There is no milky fluid, no watery gel that pours out, and no colour change on cutting beyond the darkening of the exposed surface as it dries. The smell is faint and earthy at most.

That single property, real rubberiness rather than brittleness, removes the entire Peziza-type cup group, whose flesh is fragile and snaps cleanly when bent.

Attachment and substrate

Trace the base. The stalk narrows to a point of attachment on wood — a fallen hardwood stick or small branch, often decorticated, frequently half-buried in leaf litter or moss so that the connection is not obvious until you lift it. Brushing the litter aside and confirming wood beneath is a required step, because it separates this from the terrestrial black cups that arise from soil.

The fungus is a saprotroph, breaking down the wood of fallen deciduous branches. It occurs in moist, shaded woodland, particularly along stream banks, in ravines and on north-facing slopes where the litter stays damp. It is best known from eastern North America, where it is a familiar find in mixed hardwood forest.

Season

Fruiting begins in late spring, peaks through early and mid summer, and can continue sporadically into autumn in wet years. That timing is useful, because the most similar-looking cups are on distinctly different schedules: Devil's Urn is an early spring fungus that is usually finished before Galiella starts, while Black Bulgar is an autumn and winter species.

Spore deposit and microscopy

Being an ascomycete, it fires its spores upward from the disc rather than dropping them from below, so the technique is different from a gilled fungus. Set a fresh cup disc-upwards under an inverted glass or in a covered dish with a slide suspended a centimetre above it, and leave it for several hours. A fresh, actively discharging fruitbody may also puff visibly if you breathe on it or bring it into warm air, releasing a faint smoke of spores.

The deposit is whitish. Under the microscope the spores are large and distinctive: ellipsoid, hyaline, roughly seventeen to twenty-five by nine to twelve micrometres, with a surface roughened by low warts, ridges or fine reticulation rather than smooth. Asci are cylindrical with eight spores in a row, and the paraphyses are slender and often brownish at their tips, contributing to the disc colour.

Separating it from the closest look-alikes

Bulgaria inquinans, Black Bulgar, is the closest in feel because it is also gelatinous and rubbery. Its fertile disc is black and shiny like wet tar, not reddish-brown, its outer surface is brown and scurfy-granular rather than densely hairy, it is top-shaped with a broad flat top and no real stalk, and it drops a black spore deposit. It appears on recently fallen oak and other hardwood, mainly in autumn.

Urnula craterium, Devil's Urn, is larger and deeper — a true goblet up to eight or ten centimetres tall — with a long tapering stalk, a fringed and toothed rim, blackish-brown interior and exterior, and leathery rather than gelatinous flesh. It fruits in early spring on buried hardwood.

Sarcosoma species are larger still, globose to bowl-shaped, and packed with a watery gel that runs out when they are cut; they are spring species usually associated with conifers.

Wolfina aurantiopsis is comparable in build but has a paler orange to ochre exterior and a less densely hairy outer surface.

Plectania and Pseudoplectania species have thinner flesh, blackish or dark olive discs, and are typically early-season.

Peziza species and other true cup fungi are settled by the bend test: their flesh is brittle and snaps, they lack the black hairy exterior, and most sit directly on soil, litter or dung.

A field routine

Summer, damp hardwood woodland, dark cups clustered along a fallen stick; blackish, densely hairy outside; smooth reddish-brown inner disc; squeeze and get rubber, not crumbs; cut and find thick translucent gelatinous flesh; confirm wood beneath the litter; deposit whitish with large warted spores. That run of checks lands on Galiella rufa without ambiguity.