Common Earthball Identification Guide

The setting and the first impression

You find the Common Earthball with your boot as often as with your eyes. The typical scene is a patch of thin acid soil under birch or oak, a mossy bank, a heathy woodland edge, or the sandy shoulder of a forest track. Sitting half-buried in the litter is a hard, dirty-yellow ball the size of a golf ball or a small orange, with no stalk to speak of and no obvious cap or gills. It feels like a potato: dense, firm, and heavy for its size. That solidity is the first and best character. A puffball of the same size gives under thumb pressure like a marshmallow; Scleroderma citrinum barely yields at all.

Reading the outer wall

Look at the rind, or peridium, in good light. The ground colour is a dull ochre-yellow to buff, sometimes greying or browning with age and weather. It is covered in coarse, irregular, wart-like scales that are darker brown at their tips and often arranged in a cracked, mosaic-like pattern with pale fissures running between them. On old or rain-washed specimens the scales flatten and the surface becomes areolate, like dried mud.

Now feel the thickness. Press a thumbnail into the wall and, better, cut a wedge out with a knife. The rind of this species is thick and stiff, commonly one and a half to four millimetres, and it stays rigid rather than flexible. Cut surfaces of the rind are white and often flush pink to reddish over a minute or two, then dull. That thick, rigid, pinking rind is a proper diagnostic feature.

The interior in section

Cutting the ball cleanly in half is not optional; it is the identification. There is no stipe, no gills, no pores, and no separate spore-bearing surface, so the interior is where the information sits.

In a very young specimen the whole interior is firm and white to pale pinkish grey. As it develops, the spore mass, or gleba, turns a striking purple-black to blackish-violet, and is characteristically marbled with fine whitish veins of sterile tissue that make a marbled or granite-like pattern in cross section. That purple-black-with-white-marbling stage is the classic look and the one you should try to see. At full maturity the gleba dries to a loose, powdery, olive-brown to dark brown dust, and the rind splits irregularly across the top so that wind and rain can lift the powder away. Old, emptied earthballs sit around as cracked cups long after the season.

Base and attachment

There is essentially no stalk. The ball narrows abruptly at the bottom into a wrinkled, folded, off-white pad or a very short stalk-like point, and from that point a mat of thick white to yellowish mycelial cords runs out into the soil and litter, often with sand grains, moss and rootlets cemented on. Lift a specimen carefully with a trowel rather than pulling it, because the presence or absence of a genuine tapered sterile base, and the character of the cords, feeds directly into separating the earthball species from one another.

Flesh and colour change

Away from the rind there is no true fleshy tissue to describe, but note reactions anyway. Freshly cut rind reddens or turns pinkish in many collections. The immature white gleba may darken and discolour slowly on exposure. There is no latex and no blueing.

Spores and how to examine them

An earthball is a gasteroid fungus: the spores mature inside a closed ball and are never dropped from a hymenium, so a conventional spore print is impossible. Do not waste an hour trying. Instead, take a mature, cracked specimen, tap it over a sheet of white paper, and look at the powder: dark olive-brown to blackish brown, dry and dusty, drifting easily. If you have a microscope, the spores are globose, thick-walled, and covered in a coarse net-like reticulum or spines, which is quite different from the smooth or minutely warted spores of true puffballs.

Substrate, season and ecology

Scleroderma citrinum is ectomycorrhizal, forming sheathing partnerships with tree roots, so it is always found under or near trees rather than out in open grass. Birch, oak, beech, pine and other broadleaf and conifer hosts all support it. It prefers acid, sandy or peaty ground, mossy banks, heathland edges and disturbed woodland soil, and it will fruit on nearly bare mineral soil where the litter layer is thin. The main season is midsummer through late autumn, with fruit bodies persisting for weeks because the tough rind resists decay.

One ecological detail is worth watching for: a small bolete, Pseudoboletus parasiticus, sometimes erupts in a cluster directly from the side of a living earthball. Finding a stalked, yellow-pored bolete apparently growing out of a hard yellow ball is not a puzzle, it is a confirmation of the host.

Separating it from the look-alikes on morphology

True puffballs (Lycoperdon, Bovista, Calvatia). The rind is thin, soft and flexible, not thick and rigid. The interior of a young puffball is pure white and marshmallow-soft with no purple-black marbled stage, and many have a distinct sterile base that stays spongy after the top has turned to spore dust. Mature puffballs open by a neat apical pore rather than splitting raggedly. Lycoperdon perlatum is also pear-shaped with a tapering stalk-like base and is covered in detachable conical spines, not warty scales.

Scleroderma verrucosum. The rind is much thinner, often under a millimetre, the scales are finer and browner, and there is a well-developed, wrinkled, stalk-like sterile base with prominent cords. Overall it looks browner, more delicate and more clearly stalked.

Scleroderma areolatum. Smaller, with a thin rind and a distinctive pattern of small dark dot-like scales set in pale areolate cracks, and a slender stalk-like base.

Scleroderma bovista. Smoother, thinner-walled and more elastic, often with a papery-looking surface and a tapering base with strong cords.

Pisolithus arhizus. Much larger, club-shaped rather than round, with a stalk-like base, and in section it is full of pea-like peridioles set in a dark matrix that ripen from the top downward.

Earthstars (Geastrum, Astraeus). The outer wall splits into rays that peel back to leave a central sac with a pore, a structure no Scleroderma ever produces.

Truffles and false truffles. These are wholly underground with marbled or veined interiors, but lack the thick warty ochre rind and the loose powdery dark spore mass of a mature earthball.

Working sequence in the field

Confirm hardness by squeezing. Confirm the ochre, coarsely warted rind. Cut it in half and look for a thick rigid wall around a white-marbled purple-black gleba. Check the base for a pad of cords rather than a spongy sterile stalk. Confirm woodland with trees rather than open lawn. Those five checks resolve most collections.