Toothed Cup Identification Guide

The Setting You Are Standing In

Toothed Cup is a species you find on your knees. It grows on bare, damp, compacted earth: the scraped edge of a woodland path, a clay bank above a ditch, the sides of a rabbit scrape, the soil thrown up by a fallen root plate, or the trodden margin of a track through a wood. Ground that has been disturbed and left open — with little or no vegetation and a firm mineral surface — is exactly the right search image. It leans toward calcareous and loamy soils but is not fussy.

The first impression is deliberately unremarkable: a scatter of small, pale, greyish objects the size of a pea or a shirt button, sitting singly or in loose groups, half sunk into the soil so that only the rim shows clearly. Many people walk past them entirely. Once your eye is in, they are easy to pick out because the pale interior catches light against dark earth like a set of tiny cups set into the ground.

Reading the Cup

Start with the profile, because shape does most of the work in this genus. Fruitbodies are 0.5 to 1.5 cm across and consistently deep — hemispherical to distinctly goblet- or urn-shaped, with the walls curving up and inward. The key point is that the cup stays deep. It does not flatten out into a saucer or disc as it matures, and even fully developed specimens keep an obvious hollow with a narrow opening relative to their depth.

The inner surface — the fertile hymenium — is smooth, even and pale: greyish-cream, pale buff, whitish-ochre, occasionally with a faint olive or drab tint in damp weather. It is matt rather than shining. There are no veins, wrinkles or ribs.

Now the margin, which gives the species its name. Look at the rim with a hand lens. It is not smooth or torn but regularly and finely toothed, carrying a series of small, whitish, blunt to triangular teeth or crenulations spaced evenly around the entire circumference. The teeth are usually paler than the rest of the fruitbody and stand out against the interior. On a fresh specimen the effect is like a tiny crown or a pinked edge.

The Outer Surface, Base and Flesh

Turn a fruitbody over — or better, ease one out of the ground with a knife blade so the base comes intact. The outer surface is paler than the inside, whitish to pale buff, and distinctly furfuraceous: covered in a fine granular, mealy or bran-like scurf that you can feel as a slight roughness and see clearly with a lens. It is never smooth and glossy, and never hairy in the sense of bearing long stiff bristles.

The base narrows into a short, thick, stem-like point, usually buried, whitish, and clothed in white mycelial down that mats soil particles around it. Because the fruitbody sits so low, this rooting base is often the only part not visible from above, and it is worth excavating to confirm.

The flesh is very thin — under a millimetre — whitish, and brittle. It snaps rather than bending. Cut a fruitbody in half and the section stays uniformly pale: there is no latex, no juice, no bruising and no colour change of any kind, in the cup wall or at the base.

Taking a Spore Deposit

Being an ascomycete, this species fires its spores from asci rather than shedding them passively. To collect a deposit, invert a mature cup over dark card inside a sealed, humid container and leave it several hours; the print is white and sparse, and invisible on white paper.

A better field trick is to warm a fresh cup by breathing on it, or to jolt it lightly with a fingernail. A synchronised discharge often produces a small visible puff of white spores from the fertile surface, which confirms the group instantly.

With a microscope the species becomes much more secure. The spores are smooth, broadly elliptical and large for such a small fruitbody — roughly 20 to 24 by 12 to 14 micrometres — and each contains two conspicuous oil droplets. That combination of large, smooth, two-guttulate spores together with the toothed margin and mealy exterior places a collection in Tarzetta with confidence.

Substrate and Season

This is a soil saprotroph. It lives on and in bare mineral and humic soil, breaking down organic matter in the top few centimetres, and it does not fruit on wood, dung or burnt ground. Disturbance seems to favour it: path cuttings, banks, ditch sides, quarry spoil that has begun to weather, and the bare earth under dense scrub or hedge bottoms.

Fruiting runs broadly from spring through autumn, with peaks after prolonged rain when bare ground stays damp for several days. Fruitbodies appear scattered or in small groups rather than in dense swarms, and they persist for a week or two before collapsing. Established sites often produce fruitbodies year after year in the same few square metres.

Separating the Look-alikes on Structure

Tarzetta catinus — the immediate confusion, and the same genus. It is significantly larger, commonly 1.5 to 4 cm across, and it opens out with age into a broad, shallow, flaring goblet or saucer with a wide mouth, on a stouter stalk-like base. T. cupularis stays small and stays deep, keeping a narrow opening. If a fruitbody has expanded into something you could rest a coin flat in, it is not cupularis.

Geopyxis carbonaria — also toothed at the margin and stalked, but it fruits on burnt ground, is thinner and more fragile, and has a warmer reddish-tan to orange-brown interior with a paler, often whitish toothed rim contrasting sharply against it. Habitat alone usually settles this one.

Humaria hemisphaerica — similar size and deep cup shape on soil, but the interior is a clean chalky white and the outer surface is clothed in stiff, dark brown hairs that project beyond the rim as a bristly fringe. Under a lens the difference between a hairy fringe and blunt whitish teeth is obvious.

Peziza species — generally larger, usually broader than deep, brown to olive-brown or violet-tinged, with a smooth or scurfy but untoothed margin and no stem-like base.

Cheilymenia and other eyelash cups — brightly orange or red, with conspicuous long dark marginal hairs, and typically on dung or rotting vegetation.

Otidea species — brown, upright and ear-shaped, split down one side, never forming a closed circular cup.

A Working Checklist

1. Bare, damp, compacted or disturbed soil — path edges, banks, ditch sides.
2. Small fruitbody, 0.5 to 1.5 cm, staying deep and goblet-shaped.
3. Pale greyish-cream smooth interior, matt, unveined.
4. Margin evenly toothed with small whitish crenulations.
5. Outer surface whitish and finely mealy or granular.
6. Short buried stem-like base with white mycelial down; thin brittle white flesh with no colour change.