Pixie Cup Lichen Identification Guide

First impressions and the setting

Pixie Cup Lichen is found at ground level, usually on your knees. The typical setting is a bank of thin, mossy, acid soil: a heathland edge, a woodland ride, an old wall top with a soil cap, a gravelly track verge, a rotting stump or a mossy boulder ledge. The lichen forms a low mat, and above the mat stand short grey-green goblets, generally 5-20 mm tall and 3-10 mm across the mouth.

The first impression is of tiny stemmed wine glasses or golf tees scattered over a scaly green-grey crust. Because these are lichens rather than mushrooms, they persist year-round and do not appear and vanish with the weather, though they swell and brighten when wet and shrink to a grey-khaki crust in drought.

Understanding the two-part body before you start

Getting Cladonia identifications right depends on reading two structures separately.

The first is the primary thallus, the mat of small leaf-like scales called squamules lying on the substrate. In Cladonia pyxidata these squamules are well developed and persistent, 1-4 mm long, grey-green to olive above and conspicuously white beneath, often with slightly upturned or crenate margins. Turn a few over with a pin; the sharp white underside is normal.

The second is the podetium, the upright stalked structure that carries the cup. Everything from here on is about the podetium's shape and surface, so keep the two in your notes as separate observations.

Reading the podetia and cups

Podetia rise directly from the squamule mat. In this species they are short and stout, expanding fairly abruptly and evenly into a regular goblet, so the outline is a clean trumpet rather than a long thin stalk with a small flare on top. The cup is usually as wide as, or wider than, the stalk is tall, which gives the species its squat proportions.

Now put a hand lens on the outer wall of the cup and on the inside of the goblet. The surface should be corticate, meaning covered with a continuous skin, and roughened with coarse granules and small warts. Under magnification these look like scattered grains of sugar or minute knobs, and each granule is itself corticate and shining rather than powdery. Some specimens also carry small squamules climbing the podetium wall.

That granular but corticate surface is the crux of the identification. Rub the cup gently with a fingertip. Nothing comes away as a dust or a smudge; the granules stay put. In the closely related species the cup surface is coated instead with soredia, a fine powdery farinose bloom that smears and looks like flour or dry paint dust under the lens.

Check the cup floor too. In Cladonia pyxidata it is typically closed, or if perforated then only narrowly so, and it is also granular-corticate. Wide gaping holes in the cup base point elsewhere.

The fertile surface and why there is no spore print

The fruiting bodies here are apothecia, small dark red-brown discs borne on the rim of the cup, sometimes stalked on short proliferations that grow up from the margin. They are often absent, so their presence confirms but their absence proves nothing.

A spore print, the workhorse test for gilled mushrooms, is not part of this workflow. A lichen releases its spores from asci embedded in these tiny apothecial discs rather than from an exposed hymenium below a cap, and the discs are too small and too slow to yield a visible deposit on paper. Substitute two other observations. First, examine the apothecial rim with a lens for colour, which is a consistent dark chestnut to red-brown rather than black or pale. Second, note whether the cup margin proliferates, producing a second tier of small cups sprouting from the rim of the first. Occasional single proliferation happens in this species but repeated stacked tiers are more typical of relatives.

Spot tests are the standard laboratory follow-up if the material is ambiguous, since the group is separated largely on secondary metabolites, and Cladonia pyxidata reacts PD positive red and K negative. Note that as a confirmation step, not a field one.

Substrate, season and ecology

This is a terricolous pioneer. It grows on nutrient-poor mineral or humic soil, on peaty and sandy banks, in rock crevices where soil has accumulated, over mosses, on the tops of old walls and on decaying wood such as stumps and fence posts. It tolerates a wide pH range but is most abundant on acid to neutral substrates, and it is a colonist of disturbed, thin, open ground rather than closed vegetation.

It is a partnership of a fungus and a green alga, so the whole structure photosynthesises. That means it needs light, and dense shade or a growing sward will eventually crowd it out. It is present all year, and the practical seasonal advice is to look after rain, when the squamules swell, the cups fill out and the green tones return, making everything far easier to read under a lens.

Separating it from look-alikes on morphology alone

Mealy Pixie Cup (Cladonia chlorophaea group). The main confusion, and it is a genuinely difficult one. Its cups are coated in fine granular to farinose soredia that smear when rubbed, whereas Cladonia pyxidata has coarse, corticate granules that do not. Under a lens the chlorophaea surface looks dusty and matt; pyxidata looks warty and slightly shining. This is an aggregate of chemically defined species, so field separation is a matter of stating the more likely option and confirming later.

Trumpet Lichen (Cladonia fimbriata). Much more slender and elegant, with a long smooth stalk flaring only near the top into a narrow cup, and the entire podetium is coated in fine white-grey farinose soredia. The proportions alone usually settle it: fimbriata is a champagne flute, pyxidata is a squat goblet.

Cladonia pocillum. The closest morphological match, with similar granular-corticate cups. Separate it by the primary thallus, which in pocillum forms a tight, closely appressed rosette pressed flat to the substrate, and by its preference for calcareous soils over limestone or mortar. Cladonia pyxidata has looser, more ascending squamules and prefers acid ground.

Cladonia gracilis and other stalked species. Taller, more cylindrical podetia with small or absent cups, smooth to scaly surfaces, and a primary thallus that often disappears with age.

Cup-shaped ascomycetes and moss capsules. At a glance a wet moss sporophyte or a small brown cup fungus can be mistaken for a pixie cup, but neither has the grey-green photosynthetic surface, the persistent squamule mat, or the year-round persistence.

A quick field sequence

Mat of grey-green squamules, white below, on thin acid soil, wood or a mossy bank. Squat goblet podetia rising from it, cups broad relative to stalk height. Lens shows coarse corticate granules, not powdery soredia, on cup interior and exterior. Cup floor closed or narrowly perforate. Any apothecia dark red-brown on the rim. That combination identifies the Pixie Cup Lichen.