Giant Puffball Identification Guide

The Shape You See From Fifty Paces

Almost nobody finds this species by peering into the grass. You notice it from across a field: one or several white spheres sitting on close-cropped turf, bright enough that the first guess is usually a stray ball, a lump of chalk or a plastic bag. The setting is the giveaway as much as the object. Calvatia gigantea is a grassland fungus of enriched ground - grazed pasture and paddock margins, the nettle-choked bottom of an old hedge, parkland turf, cemetery and orchard grass, roadside verges, the edges of manured arable fields. It sits directly on the soil surface with no stem raising it, no litter covering it, and no wood involved.

Note the arrangement before you touch anything. Fruit bodies often come in lines, arcs or scattered rings, and the same arc reappears in the same field year after year because the mycelium below is long-lived and slowly expanding. A line of five white balls along a hedge bank is a far stronger observation than a single ball, and it is worth photographing the whole scene before you crouch down.

Sizing and Shaping the Fruit Body

Diameter runs from about 10 cm in a young or stunted example up to 50 or 70 cm in a good one, and outliers larger than a beach ball are recorded. Shape is globose to slightly flattened, sometimes a little pear-shaped or lopsided where it has pushed against a tussock, but there is never a distinct stalk and never a stem-like sterile column lifting the head clear of the ground.

Roll it gently. The whole thing is attached to the soil at a single small point by a tough white cord of mycelium - a root-like strand a few millimetres thick. When you lift a mature one it detaches easily and leaves a pale disc of bound soil and grass roots. That single-point attachment, with no tapering base, is a solid structural character.

The Skin

Feel the outer wall, or peridium. Fresh, it is smooth, matt and slightly yielding, with the texture of soft kid leather or fine suede; there are no spines, no warts, no pyramidal scales, and no coarse cracking pattern. Colour is white to ivory when young. As the fruit body matures the skin dulls through cream to ochre-buff, then dingy olive-brown, and it commonly develops shallow felted patches or fine cracks in dry weather.

Ageing is destructive rather than tidy. Instead of opening by a neat pore at the top the way a Lycoperdon does, the skin of a giant puffball tears, flakes and peels away in irregular sheets, exposing the mass of spores beneath to the wind and rain until only a brown ragged bowl of tissue is left in the grass. Those weathered brown remnants sit around all winter and are worth learning, because they tell you where to look the following autumn.

The Vertical Cut - the Single Most Useful Test

Whatever the size, slice the fruit body from top to bottom with one clean stroke and look at the cut face. This one action separates a puffball from most of the things that imitate one.

In a young giant puffball the interior, the gleba, is pure white, uniform and firm all the way through. There is no structure in it at all: no chambers, no marbling, no dark veining, no outline of a cap or gills, no gelatinous layer. It should look like dense white foam right out to the skin.

As the fruit body matures the gleba passes through cream, then yellow, then yellow-olive, then a dull olive-brown, and its texture changes from firm to cottony to a dry powder threaded with fine fibres. There is essentially no sterile base - at most a small pad of tissue at the point of attachment, not the spongy stem-like plug of many relatives.

Three failure modes are caught instantly by the cut. If the interior shows the silhouette of a miniature mushroom - a small cap, a line of gills, a central stipe - you have the unopened button of an Amanita or a related agaric, not a puffball at all. If the interior is firm and dark purple-black with a white marbled net, and the rind is thick and rubbery, you have an earthball, Scleroderma. If there is a distinct spongy sterile stalk below a chambered fertile head, you are in Lycoperdon or a puffball relative rather than Calvatia gigantea.

Spores and How to Sample Them

Puffballs do not produce a classic gilled-mushroom spore print, because the spores are not shed onto a surface below - they are released as a cloud when rain, wind or a footstep compresses the mature fruit body. To record spore colour, tap a little powder from a mature specimen onto white card: it reads olive-brown to dull yellow-brown in mass. Under a microscope the spores are globose, roughly 3.5-5.5 micrometres, minutely warted, and mixed with long, branched, thick-walled capillitial threads that give the old gleba its cottony feel.

Substrate, Season and Ecology

Calvatia gigantea is a saprotroph, breaking down organic matter in soil rather than partnering with tree roots, so it needs no particular tree overhead. It favours nitrogen-rich, well-manured or otherwise enriched grassland; the presence of dense stinging nettle along a hedge is a reliable indicator of the same soil conditions. The main flush comes in late summer and autumn, usually a week or two after a substantial soaking followed by warm weather, and a colony can go several seasons without fruiting before producing a dozen fruit bodies at once.

Separating the Look-alikes on Morphology Alone

• Other Calvatia. Calvatia booniana, of western North American dry country, reaches a comparable size but its skin is divided into distinct flat polygonal warts and patches rather than staying smooth. Calvatia cyathiformis is goblet- or pear-shaped with a well-developed sterile base that persists as a cup after the top blows away, and its mature gleba is purple-brown rather than olive-brown. Calvatia craniiformis is smaller, skull-shaped and wrinkled, tapering to a chunky sterile base.
• Lycoperdon and Apioperdon. Far smaller, usually under 6 cm, with spiny, granular or mealy skin, a well-defined sterile stalk-like base, and a neat apical pore through which the spores puff.
• Bovista. Small, becoming loose and rolling free of the ground, with a papery inner wall that peels away from a thin outer skin.
• Scleroderma (earthballs). Rind 2-4 mm thick and hard, surface coarsely scaly, interior firm and purple-black with a white marbled pattern from an early stage, and the whole thing usually half-buried among tree roots rather than sitting on open turf.
• Agaric buttons. Any unexpanded gilled mushroom is settled by the cut test described above.