Pear-shaped Puffball
Apioperdon pyriforme
Also called stump puffball
A small, smooth, pear-shaped puffball that fruits in crowded troops directly on rotting stumps and logs, joined at the base by conspicuous white mycelial cords. It is the only common puffball reliably found on wood.
Overview
The Pear-shaped or Stump Puffball is the wood-inhabiting member of the puffball group, and its habit alone separates it from almost every relative. Where other puffballs sit singly or in loose troops on soil, this species erupts in dense colonies - sometimes dozens or hundreds of fruiting bodies - carpeting the top and sides of a decaying stump.
Long placed in Lycoperdon, it has been segregated into the genus Apioperdon on molecular grounds, though the older name Lycoperdon pyriforme remains in wide use. The specific epithet refers to the pear-like outline: a rounded fertile head tapering into a short, narrower, wrinkled base.
It is a valuable indicator of late-stage wood decay. By the time it fruits, a stump is usually soft, crumbling and well colonised, and the puffballs often appear alongside other decomposers on the same piece of timber.
How to identify it
Fruiting body
Small, 1.5-4.5 cm wide and up to about 4.5 cm tall, shaped like a pear, a top or a rounded pestle: a swollen head narrowing abruptly into a short pinched base. Whitish to pale cream when young, quickly becoming buff, yellow-brown and finally dull brown with age.
Surface
Much smoother than the Gem-studded Puffball. The young surface bears only fine granules, minute warts or a fine granular scurf which soon wears away to leave a nearly smooth, slightly leathery skin. There are no tall conical spines and no net-like scar pattern.
Base and mycelial cords
The defining feature: thick white cord-like rhizomorphs radiate from the pinched base into the rotten wood beneath, often clearly visible when a cluster is lifted or when the fungus grows on an exposed stump face. Fruiting bodies frequently crowd shoulder to shoulder and become mutually flattened.
Interior and spore print
The gleba is white and firm at first, ripening through olive-yellow to a dry olive-brown powder released through a small apical pore that tears open at maturity. The sterile base remains spongy and paler. Spore print olive-brown; spores smooth to very finely roughened and spherical.
Where and when it grows
This species is a wood decomposer, fruiting on rotting stumps, fallen logs, large buried roots and sawn timber of both broadleaf and coniferous trees. It is especially frequent on old beech, oak, birch and pine stumps, and occasionally appears to grow from soil when it is in fact colonising wood buried beneath the surface - the white mycelial cords, if traced down, lead to the hidden substrate.
Fruiting is late in the season, from late summer through autumn and often continuing into early winter after other fungi have finished. Weathered brown husks can persist on the same stump until spring. It is common and widespread throughout temperate Europe, North America and Asia.
Ecological role
Apioperdon pyriforme is a saprotroph specialising in the later stages of wood decay. Its mycelium spreads through already-softened, well-rotted timber, and the conspicuous rhizomorph cords allow it to transport water and nutrients across the substrate and to colonise fresh pieces of wood nearby. Fruiting in dense colonies from a single interconnected mycelial network is why the puffballs appear in such crowded, uniform troops.
By breaking down lignin and cellulose in dead wood, the fungus helps convert standing stumps into soil organic matter, releasing carbon and mineral nutrients back into the woodland system. Its late-season fruiting extends the period of spore release into the cold months, when raindrops striking the elastic wall continue to puff spores from the apical pore.
Similar species
The Gem-studded Puffball (Lycoperdon perlatum) is the main confusion. It grows on soil and litter rather than wood, is larger and more elongated, carries prominent detachable conical spines that leave net-like scars, and lacks the thick white basal cords. Where the two occur near each other, substrate plus surface texture settles it.
The Spiny Puffball (Lycoperdon echinatum) is a soil species with long dark curved spines. The Meadow Puffball (Lycoperdon pratense) is a grassland fungus, squatter, and shows an internal membrane between fertile and sterile parts in vertical section. Young earthballs (Scleroderma species) are tougher, thicker-skinned and coarsely scaly, sit on soil without a pinched base, and their interior blackens early rather than staying white then ripening to brown powder.