Pepperpot Earthstar
Myriostoma coliforme
Also called salt-shaker earthstar, many-mouthed earthstar, sieve earthstar
The only earthstar with a spore sac perforated by many mouths and propped on a cluster of little columns, like a pepper pot on legs. A scarce, unmistakable species of dry sandy ground.
Overview
Myriostoma coliforme is the sole widely recognised member of its genus and is instantly separable from every other earthstar by two features no Geastrum possesses: the spore sac is pierced by numerous mouths rather than one, and it is raised on a group of short stalks instead of a single column or none at all. The generic name means "countless mouths" and the epithet likens the perforated sac to a sieve.
Like other earthstars it belongs to the family Geastraceae. The young fruiting body is an onion-shaped ball buried or half-buried in the soil; as it matures the outer wall splits from the apex into rays that peel back and lift the inner sac clear of the ground. Only then does the definitive multi-holed structure become visible.
The species is uncommon to rare through much of its range and is red-listed in several European countries, where it is associated with old, undisturbed sandy banks and hedge bottoms. Where it does occur it often fruits in the same spot for years, and the weather-beaten old stars can persist long after spore release.
How to identify it
Fruiting body
Emerges as a buried, onion- or top-shaped ball 2–5 cm across, then splits into typically 5–12 rays that spread or arch to form a star 3–12 cm wide. Rays are fleshy at first, drying leathery, buff to grey-brown, often with soil and sand adhering below.
Spore sac
The central sac is 1–4 cm across, roughly spherical to slightly flattened, silvery grey to bronze or pale coffee-brown, and finely roughened or minutely scurfy. Its defining feature is the scattering of many small, irregular round mouths over the upper half — from a handful to dozens — each a separate opening for spore escape.
Stalks
Beneath the sac sits a cluster of several short, stout columns (a few to around a dozen), pale and often flattened, that hold the sac slightly above the ray disc. No other earthstar has this multiple-columned base; Geastrum species are either sessile or set on a single pedicel.
Flesh & spores
The young interior is firm and white, ripening to a powdery brown spore mass mixed with branched capillitium threads. The deposit is brown; spores are globose and warted under magnification.
Where and when it grows
This is a fungus of warm, dry, free-draining ground. It turns up on sandy soils along hedgerows and field margins, on old banks, in open broadleaf woodland edges, on riverside sand deposits and occasionally in churchyards, parks and gardens on light soil. It is frequently reported near elm, ash, poplar, oak and other broadleaved trees, and often in nutrient-enriched spots such as long-established hedge bottoms.
Distribution is scattered and patchy across Europe (where it is considered threatened in many countries), and it is also recorded from North and South America, Africa, Asia and Australasia. Fruiting bodies typically appear from late summer through autumn, though the tough dried stars often survive on the ground well into the following year.
Ecological role
Myriostoma is generally regarded as a saprotroph, breaking down organic matter and buried plant debris in sandy soils and humus-rich hedge bottoms rather than forming root partnerships. Its mycelium develops underground, and the fruiting body pushes up and unfolds only when mature.
Spore dispersal is by puffing: raindrops, falling debris or animal contact compress the thin-walled sac, and dry spores are expelled in fine clouds through the many mouths. The multiple openings and the raised, stilted position of the sac both help catch air movement and spread spores more widely than a single pore would allow. The persistent, weathered fruiting bodies can keep shedding spores for a long period.
Similar species
Any Geastrum earthstar can suggest this species at a glance, but the test is simple: look at the sac. Geastrum triplex, G. fimbriatum, G. rufescens and their relatives all have exactly one mouth, and their sac is either sessile or perched on a single short column. Myriostoma has many mouths and a cluster of columns.
Geastrum fornicatum also raises its sac well off the ground, but it does so by arching four rays like a stool and still has one apical opening on a single pedicel. Old, collapsed puffballs such as Lycoperdon species can look perforated when torn by weather, but they lack any star of rays and have a continuous, papery wall with one ragged tear rather than tidy round mouths. Weathered Astraeus hygrometricus has thick, cracked, moisture-responsive rays and a sessile sac with an irregular slit.