Star Earthball

The Star Earthball is the most theatrical member of Scleroderma. It begins as a hard, whitish, almost stone-like ball buried in compacted ground, swelling until it forces the soil crust apart. The thick rind then splits from the top into several stiff, blunt, unequal rays that curl back, so that a mature specimen sits in the earth like a pale opened hand — the origin of the alternative name Dead Man's Hand.

Despite the star-shaped opening it is not an earthstar: there is no separate papery inner spore sac and no pore. The rays are simply the torn wall of a single-layered earthball, and the dark spore mass lies exposed in the bowl they form, gradually weathering away.

A dense mass of white mycelial cords at the base gives the species its epithet polyrhizum, "many-rooted", and helps anchor these heavy fruit bodies in the hard, often bare ground they favour.

Fruiting body

Unopened specimens are 4–12 cm across, subglobose to somewhat flattened, hard and heavy, dull whitish to pale buff or greyish-brown, with a surface that is smooth to finely cracked, scurfy or areolate. They develop partly or wholly buried, so the exposed top is often stained with soil.

Opening and rays

At maturity the wall splits from the apex into roughly 4–10 thick, stiff, irregular rays. These are pale on the inner face and recurve or arch back, sometimes lifting the whole structure slightly clear of the soil. The rays are woody-tough and can persist through the winter long after the spores have gone.

Wall and spore mass

The rind is notably thick — often 3–8 mm — white in section and firm to almost corky. The gleba begins white and solid, then becomes marbled purplish-grey with pale sterile veins, and finally ripens to a dry, dark brown to blackish spore powder that fills the shallow cup of the opened fruit body.

Base

The base tapers into a compact mass of white to buff rhizomorphs that bind soil, stones and grit into a firm plug, so that lifting a specimen usually brings up a lump of substrate with it.

This species is characteristic of hard, poor and disturbed ground: bare compacted soil, roadside verges, gravelled tracks, sandy waste ground, lawn edges, pastures and the margins of parking areas. It often appears where the ground is too trodden or too dry for a dense turf, pushing up through a crust of soil.

Fruiting runs from summer into autumn, and the tough opened remains can be found at almost any time of year. The Star Earthball is widespread in warm-temperate and subtropical regions and is especially frequent in the southern and central United States, southern Europe, Mexico and parts of Asia and Australia.

Scleroderma polyrhizum is ectomycorrhizal, associating with oak and other broadleaf trees, though its fruit bodies frequently appear in seemingly open ground some distance from an obvious host — the rhizomorph network can run a considerable way from the partner roots. In the poor, compacted soils it favours, that partnership improves the tree's access to water and phosphorus.

The fungus matures hypogeously, completing spore development while still buried, and only exposes the gleba once the wall ruptures. Dispersal is then entirely passive: wind strips the dark powder from the open bowl and rain splash carries the rest into the surrounding soil.

Earthstars (Geastrum species) also open into rays, but their rays are thin, leathery and flexible, and they reveal a distinct papery inner spore sac that releases spores through a defined apical mouth. The Star Earthball has no inner sac at all — just torn, thick rind around exposed spore dust.

Other earthballs are separated by size and rind thickness: the Common Earthball (Scleroderma citrinum) is smaller, yellower, coarsely warted and tears irregularly rather than into neat thick rays, while the Potato Earthball (Scleroderma bovista) is small, pale and thin-walled. Unopened specimens of S. polyrhizum can suggest a large puffball, but puffballs are light in the hand with a soft white cottony interior instead of a hard rind and marbled purplish gleba.