Striated Earthstar Identification Guide

The First Impression

Earthstars announce themselves by shape rather than colour. You are working along a shaded hedge bank, through a nettle patch behind an old wall, in a neglected shrub border, under yew or planted conifers, or across a churchyard bank thick with old leaf mould. Pressed against the ground is a small, pale, star shaped object 2 to 5 cm across, with a rounded sac sitting in the middle of a ring of pointed rays. Because earthstars are dry, tough structures they persist for months, so it is common to find this season's fresh material alongside last year's weathered grey remains. The overall colour is buff to grey brown, and the whole thing looks more mineral than fungal until you pick one up.

The Unopened Stage

Before it opens the fruit body is an onion shaped or slightly beaked egg, whitish to buff or dirty brown, buried or half buried in humus, and usually with soil, leaf fragments and root hairs glued to the surface by the outermost mycelial layer. If you find one, cut it vertically: the section shows a thick outer wall enclosing a firm, pale interior that will later become the powdery spore mass. Splitting of the outer wall begins at the apex and proceeds downward.

The Rays

The outer wall splits into five to nine, most often six to eight, triangular pointed rays. These bend backwards and downwards, and because they push against the ground they frequently lift the central sac a little above the litter; strongly recurved rays may curl right under the body. The upper surface of the rays, which was the inner face of the egg, is pale buff to grey brown and often cracks or flakes as it dries. The rays are not markedly hygroscopic: they do not repeatedly close up when damp and reopen when dry, which distinguishes the group from some other star shaped fungi. Note also whether the rays remain attached to a cup of debris at the base, since that helps with several look-alikes.

The Spore Sac, the Stalk and the Collar

Now examine the central sac, which is 0.8 to 1.5 cm across, globose to slightly flattened, greyish to grey brown, and covered when fresh with a fine whitish frosted bloom that wears away to leave a smoother, darker surface. Two features here carry the identification.

First, the sac is raised on a short but distinct stalk. Tilt the specimen on its side, or better, slice it vertically through the middle, and you will see the sac sitting clear of the ray disc on a narrow column.

Second, where that stalk meets the underside of the sac there is a flat, horizontally spreading collar, a small saucer or shelf of tissue encircling the base of the sac. This apophysis is the feature most worth training your eye on, because it is visible with a hand lens on any well developed specimen and is absent or differently formed in the species most likely to be confused with it.

The Beak

The mouth of the sac is equally diagnostic. It rises as a sharply conical, distinctly beaked cone, clearly set off from the rest of the sac by a groove or by a paler surrounding zone, and its surface is finely and regularly grooved, with fine ridges radiating from the tip down the sides of the cone. Use a hand lens in raking light; the striations are unmistakable once seen and quite unlike the woolly, fibrous or ragged mouths of many earthstars.

Inside the Sac

Cut a mature sac in half. The interior is filled with a dry, powdery, chocolate brown spore mass shot through with fine threads, and a pale central column, the columella, runs from the base of the sac up toward the mouth. Immature material is firm and whitish inside and will not puff, so sectioning also tells you whether a specimen is ready to be examined. There is no colour change on bruising, and the whole structure is dry and papery rather than fleshy.

How the Spores Leave, and What Passes for a Print

A conventional spore print is not possible. Spores are expelled in puffs through the beak when raindrops strike the sac wall or when an animal brushes past, and you can reproduce this by tapping the sac gently with a fingertip over a sheet of dark paper to collect a brown dust. Under a microscope the spores are globose, brown and covered in coarse warts, roughly 3.5 to 5 micrometres across, and they are mixed with long, thick walled capillitial threads that help meter the spores out of the mouth over time.

Substrate and Season

This is a saprotrophic species of rich, humus laden, often disturbed soil. It favours sites with a heavy load of buried organic debris: hedge banks, nettle beds, elder thickets, shrubberies, long neglected garden ground, churchyards, and the litter under planted conifers and yew. It is not tied to any tree partner, so a sheltered, nutrient rich soil matters more than the species overhead. Fruit bodies appear from late summer through late autumn, and because they are dry and tough they persist right through winter, which makes the leafless months a good time to survey for them. They usually occur scattered or in small groups, occasionally in loose rings where a mycelium has spread evenly.

Separating It from Other Earthstars

• Geastrum pectinatum also has a stalked sac and a grooved beak, but the stalk is longer and more prominent, the beak is longer and more coarsely furrowed, the sac is often darker brown, and the whole fruit body is generally larger and more robust.
• Geastrum fimbriatum, Geastrum saccatum and Geastrum rufescens have a sac that sits directly on the ray disc with no real stalk and no collar, and their mouths are woolly or fibrous rather than finely grooved.
• Geastrum triplex is much larger, and its fleshy inner layer splits to form a broad bowl like collar around the sac at ray level. That is a different structure entirely from the small flat apophysis at the top of the stalk in Geastrum striatum, and its mouth is fibrous.
• Geastrum coronatum has a stalked, dark spore sac but its mouth is fibrillose rather than striate, so the beak settles the question.
• Geastrum fornicatum arches on long rays that lift the whole fungus off the ground on their tips, leaving a cup of debris behind, and its mouth is not grooved.
• Myriostoma coliforme is instantly separable by having several mouths on one sac and multiple supporting stalks.
• Astraeus hygrometricus has thick, leathery, cracked rays that open and close repeatedly with humidity, a sessile sac with no stalk, and no beaked, grooved mouth.

A Working Sequence

Lift one whole specimen and cut it vertically. Confirm a distinct stalk under the sac, a flat spreading collar where the stalk meets the sac, and a sharply conical beak with fine radiating grooves and a clear boundary at its base. Then check five to nine recurved rays, a greyish sac with a whitish bloom when fresh, chocolate brown powdery contents with a central columella, and a humus rich, sheltered site.