Crowned Earthstar Identification Guide

The First Impression

Autumn, a hedge bank or a shrubby corner of a churchyard or park, deep leaf litter over rich, often lime-rich soil. Among the dead leaves there is a small brown star, four to seven centimetres across, with thick fleshy arms curled back on themselves, and in the middle of it a grey ball sitting up on a short stalk. The impression is of a piece of cracked leather that has opened out and is offering something up.

Earthstars are usually found by touch as much as by eye, because they colour-match litter almost perfectly. Once you have found one, scan the surrounding half metre: they nearly always occur in small scattered groups, and having several specimens at different stages makes identification far easier.

The Unopened Stage

If you find an unexpanded one, do not discard it. Before opening, the fruitbody is an onion-shaped or bulb-shaped body with a distinct pointed beak, sitting half-buried in litter and soil. Sliced vertically, it shows the future spore mass as a firm pale interior that darkens with maturity, wrapped in the layered outer wall that will later split into rays. It is worth taking a section, because the layering visible there explains what you will see on the opened star.

Reading the Rays

Count them: normally five to nine, sometimes ten. Expanded across the tips the star measures 3 to 8 cm. The rays recurve strongly downwards, and in this species they frequently arch so far that their tips press into the litter and lever the central body clear of the ground. They do not respond hygroscopically, so a dried specimen stays open rather than folding back over the spore sac.

Now examine the layers on the ray surface, which is where the real work is done. The outermost mycelial layer carries adhering soil and debris and typically sloughs off in patches or flakes. Beneath it, the fleshy inner layer facing upwards is dark brown to almost blackish, and as it dries it cracks and peels away in irregular plates. That dark, cracking, flaking inner face on the upper side of the arms is one of the species' better characters.

Reading the Spore Sac

The central body is globose to slightly egg-shaped, 1 to 2 cm across, grey-brown and often with a distinctly leaden or bluish-grey cast. Its surface is smooth to very finely mealy; rub it gently and a fine bloom comes away on the fingertip.

Get a lens onto the junction between sac and star. Two features matter here. First, the sac is clearly stalked, raised on a short pedicel of a millimetre or two, so you can see daylight between the underside of the sac and the floor of the star. Second, at the top of that stalk there is an apophysis, a raised collar or shoulder like a small disc, where the stalk meets the sac. Together they are decisive against several similar earthstars.

Reading the Mouth

The opening at the top of the spore sac is the peristome, and its texture is the other key character. Here it is conical and fibrillose, built of fine silky fibres that converge on the pore, with no radiating grooves or pleats. It is also clearly delimited, meaning it is set off from the rest of the sac by a paler zone, a slight ridge or a shallow furrow, so the mouth reads as a distinct cone rather than merging seamlessly into the surrounding surface.

Distinguishing fibrillose from grooved takes practice. Tilt the sac into raking light: grooves are straight, evenly spaced and geometric, whereas fibres are irregular, silky and slightly matted.

Spores and the Interior

Earthstars do not produce a conventional spore print. Instead, tap a mature sac gently over dark card and a brown dust puffs out through the mouth. Cut a mature sac in half and you will find the interior powdery and dark brown, with a central sterile column, the columella, rising into it from the base; the columella is easy to see in section and is a useful confirmation that you are in this genus rather than looking at a puffball.

Under the microscope the spores are globose, coarsely warted and brown, around 4 to 6 micrometres across.

Substrate, Season and Ecology

The fungus is a litter saprotroph, working through humus and buried leaf debris rather than attacking living roots or standing wood. It favours humus-rich, often calcareous or sandy soils, and turns up under hedges, in shrubberies, on woodland edges, in old gardens and churchyards, and along tracks under broadleaf trees.

Fruiting is autumnal, but the tough outer star and the leathery spore sac persist for months. Bleached, weathered, half-buried specimens found in late winter and spring are extremely common, and while they can still be identified from ray count, stalk and mouth, fresh material is far easier to read.

Separating the Look-alikes on Morphology

The Collared Earthstar, Geastrum triplex, is much larger, and its thick fleshy layer typically cracks free to leave a distinct bowl or collar encircling the base of the spore sac; the sac itself sits directly on the star with no stalk and no apophysis.

Geastrum fimbriatum has a fibrillose mouth, but the sac is sessile and the mouth is not delimited, merging gradually into the surface of the sac; it is generally paler and smaller.

Geastrum striatum has a stalk and a conspicuous apophysis like this species, but its peristome is a distinctly beaked cone with clean radiating grooves, which is exactly the fibrillose-versus-grooved distinction described above.

Geastrum pectinatum sits on a longer, more obvious stalk and has a strongly grooved, long-beaked mouth and often a more slender overall look.

Geastrum quadrifidum and Geastrum fornicatum are arched species with a stalked sac and a delimited fibrillose mouth, but they have only four or five rays and stand on a persistent cup formed from the outer layer, which the rays remain attached to; check for that basal cup left behind in the litter.

Geastrum rufescens is sessile with a pinkish to flesh-brown tone throughout.

Puffballs and earthballs never form a star at all.

Working Checklist

• Five to nine thick rays, recurved and often arching to lift the fruitbody
• Upper surface of the rays dark brown to blackish, cracking and flaking
• Spore sac 1 to 2 cm, grey-brown with a leaden tint, finely mealy
• Sac raised on a short stalk with a distinct collar-like apophysis
• Mouth conical, silky-fibrillose, not grooved, and clearly delimited by a paler zone
• Litter under broadleaf trees and hedges on rich or calcareous soil, autumn onwards