Potato Earthball

The Potato Earthball is a modest, pale member of Scleroderma whose common name captures its habit of half-emerging from turf or sand like a small tuber. Unlike its coarsely warted relatives it is nearly smooth when fresh, developing only a fine scurf or a network of shallow cracks as it expands.

Like all earthballs it is gasteroid: the spores develop inside a closed rind and there is no cap, gill or pore layer at any stage. The fungus simply enlarges, darkens internally, and eventually tears open at the top to release dust. Its wall is thinner than that of the Common Earthball, and its base narrows into a short, folded, root-like plug rather than a true stalk.

It is a species of open, grassy and sandy ground as much as of closed woodland, and is often found along mown verges, dune systems and the trodden edges of paths where scattered trees provide a mycorrhizal partner.

Fruiting body

The ball is 2–5 cm across, subglobose to slightly flattened or irregular, dingy white to pale buff, straw or greyish-ochre. Young specimens are almost smooth to the eye and only slightly scurfy; with age the surface breaks into fine, flat, adpressed scales or an areolate network of shallow cracks, and it may bruise or discolour a dull yellowish-brown where handled or scuffed.

Wall and interior

The peridium is thin — roughly 1–2 mm — and white in section, often with a faint yellow or pinkish tinge. The gleba inside is white and firm at first, then marbled with grey and purple, ripening to a dry purple-brown to nearly black spore powder. Maturity is marked by an irregular split or a widening ragged aperture across the top.

Base

There is no proper stalk. The fruit body narrows abruptly to a small folded, sterile, root-like base from which whitish rhizomorphs run out through soil and sand, frequently gluing sand grains and grass roots into a compact plug.

Spores

Spores are dark purple-brown in mass. Under the microscope they are globose and ornamented with a partial net-like or ridged pattern rather than free spines, a feature that separates this species from its warted relatives when material is examined closely.

The Potato Earthball grows on open sandy and grassy ground: coastal dunes, dune-slack turf, mown verges, lawns with scattered trees, gravelly track edges and light woodland margins. It also occurs in open broadleaf woodland on well-drained soil, generally where the ground layer is thin and mineral soil is close to the surface.

Fruiting is mainly from midsummer to late autumn, sometimes lingering into early winter in mild coastal areas. It is widespread in Europe and North America and is recorded across temperate zones more broadly, often in more exposed situations than the woodland earthballs.

This is an ectomycorrhizal fungus, partnering with the fine roots of trees and shrubs including willow, poplar, birch, oak and, in dune systems, creeping willow. The fungal sheath and its outward-running rhizomorphs extend the effective reach of the root system into sand and thin soils that would otherwise be poor in available nutrients.

The fruit body forms just below or at the soil surface and pushes up as it swells. Spores are freed passively once the rind tears, blown out by wind or splashed by rain, and the empty rind may persist as a papery cup for some weeks afterwards.

The Common Earthball (Scleroderma citrinum) is larger and yellower with a distinctly thick rind and coarse, angular warts, while the Scaly Earthball (Scleroderma verrucosum) is finely warted and sits on a long grooved stalk-like base. The Leopard Earthball (Scleroderma areolatum) has small dark scales each surrounded by a paler ring, giving a spotted look absent in the near-smooth S. bovista.

True puffballs of the genera Lycoperdon and Bovista can look superficially similar in the field but have a soft interior that is uniformly white and cottony when young, never marbled purple, and they open by a neat apical pore rather than an irregular tear.