Pepperpot Earthstar Identification Guide

First Impression and Setting

Earthstars announce themselves by shape long before you can read any detail. You are on light, sandy, well-drained ground, typically a warm sheltered spot: a hedge bank, a river terrace with silty sand, the sparse grass under old broadleaves in parkland, or scrubby ground near buildings. Sitting on the surface is a leathery star with arching rays and, in the middle, a rounded sac a couple of centimetres across.

Myriostoma coliforme separates itself from every other earthstar with two structural features, both visible with the naked eye. The spore sac is perforated by many mouths, not one, and it is held above the star on several short legs, not on a single stalk or none. Once you have registered the sieve-like top and the little colonnade beneath, the identification is essentially finished; everything else is confirmation.

The Young Stage

Before it opens, the fruitbody is a firm, pale, bulb-shaped body sitting at or just below the soil surface, often with sand and rootlets glued to its underside. If you find one at this stage, section it vertically. You will see a thick outer wall enclosing a paler inner sac, and inside that the developing spore mass, white and firm when very immature and darkening as it matures. The multiple internal columns that will later become the legs are already forming.

The Opened Star

At maturity the outer wall splits from the top downwards into 4-12 pointed rays that bend back and outwards, lifting the central sac clear of the ground. The rays are thick and fleshy at first, drying to a tough leathery consistency, buff to ochre or greyish brown on the upper face, often cracking into irregular plates. The underside frequently retains a crust of sand and soil. Expanded fruitbodies commonly measure 4-12 cm across the outstretched star.

Because the tissue is so tough, opened fruitbodies persist for months, weathering into pale grey skeletons. That means an autumn hunt can turn up specimens from a previous season, so treat old dry material as identifiable in structure but unreliable in colour.

Reading the Spore Sac

This is the decisive organ. The inner sac is 1-5 cm across, depressed-globose, grey-brown to pale bronze or clay, and its surface is minutely granular, mealy or silvery-scurfy rather than smooth and papery.

Across the upper half sit numerous mouths, or ostioles. Count them; there are usually somewhere between five and thirty, irregularly scattered, each a small rounded or slightly torn opening with a finely fringed or ragged rim, and often slightly raised. Tapped gently, the sac puffs dust out through the many perforations at once, which is exactly where the English name comes from.

Now look underneath. The sac is raised on several short, stout, cylindrical columns, typically 3-12 of them, arranged in a loose ring where the sac meets the star. In every Geastrum you will find at most one stalk. This colonnade is unique to Myriostoma among the earthstars and is worth photographing from a low angle whenever you find one.

The Spore Mass and How to Read It

There is no spore print in the gilled-fungus sense; puffball relatives shed dust through their pores rather than dropping it from blades. Instead, hold a mature fruitbody a few centimetres above a sheet of white or dark paper and tap the sac gently. A cloud of fine snuff- to umber-brown powder falls, and that colour, brown rather than olive or purple-black, is worth noting.

Section an older fruitbody and the interior is uniformly powdery, threaded with a mesh of brown capillitium fibres and with branched columellar remnants running up from each supporting leg. Under a microscope the spores are globose, brown, 4-7 microns in diameter, and covered with coarse warts and short spines; the capillitium threads are unbranched, thick-walled and tapering.

Substrate, Season and Ecology

Myriostoma coliforme is a saprotroph of soil organic matter, not a wood-rotter and not a tree partner. It favours dry, warm, sandy or silty, often nutrient-enriched soils, and it recurs faithfully at the sites where it does occur: old hedge banks, alluvial sand near rivers, sheltered ground beneath elm, ash, oak, poplar and other broadleaves, churchyards, and disturbed ground with a stable, unshaded, free-draining substrate.

Fruitbodies form in late summer and autumn but persist so long that dried stars can be found in any month. The species is genuinely rare and locally protected across much of northern Europe, so record, photograph and leave; the fruitbody keeps releasing spores for a long time and is more useful to the population in the ground than in a box.

Separating the Look-Alikes on Morphology

Geastrum species in general are the only real confusion group. Every one of them has a single ostiole at the apex of the spore sac. If you count two or more mouths, no Geastrum is possible.

Geastrum coronatum and G. fimbriatum are similar in size and colour with recurving rays, but each has one central mouth and either a sessile sac or a single short stalk.

Geastrum triplex has a distinctive fleshy collar of tissue around the base of the sac, formed as the inner layer of the rays cracks, plus one mouth surrounded by a pale disc.

Geastrum fornicatum performs the most acrobatic version of the earthstar trick, arching on four rays that lift the body high on a raised cup, but again there is a single stalk and a single mouth.

Astraeus hygrometricus is a false earthstar with thick, tough, hygroscopic rays that fold shut when dry and reopen when wetted, and its sac tears open irregularly at one point rather than bearing neat pores.

Lycoperdon and Bovista puffballs never form rays at all; the outer wall stays as a skin on a pear-shaped or spherical body, with one apical pore.

Scleroderma earthballs have a thick, hard, scaly rind that cracks irregularly, and no star, no legs, and no organised pores.

Field Checklist

Star of 4-12 recurved leathery rays on sandy, warm, well-drained soil; central grey-brown mealy sac raised on several short columns; many fringed pores scattered over the top of the sac; brown powdery spore mass; globose warted-spiny spores. Multiple mouths plus multiple legs equals Myriostoma coliforme.