Native truffle puffball

Mesophellia glauca is one of Australia's native truffle-like fungi: not a true truffle (which belongs to the ascomycete genus Tuber) but a hypogeous basidiomycete that convergently adopted an underground lifestyle.

Its fruiting bodies are compact spheres or ovals, 2-6 cm across, sitting flush with or just below the soil surface.

In fresh, young specimens the peridium (outer skin) carries an arresting bluish-grey or glaucous bloom - the quality captured by the Latin 'glauca' - that fades to cream or pale ochre as the specimen ages and dries. The skin is smooth to very finely textured, not warty or ornamented in the manner of some similar genera.

There is no stem; the body attaches to a mycelial cord at its base.

Cutting a fresh young specimen reveals a white, firm gleba; in mature specimens the interior has converted to an olive-brown to dark brown powdery mass - the spore load.

The absence of a distinct sterile base or columella helps separate it from true puffballs (Calvatia, Lycoperdon), which have organised sterile bases in the stipe region.

The spores themselves are ellipsoid and ornamented with ridges or warts, visible under magnification.

A strict ectomycorrhizal partner of eucalypts, Mesophellia glauca is bound by biology to native Australian eucalypt forest.

It does not occur in pine plantations, improved pasture, gardens, or other modified habitats; its presence indicates a functioning eucalypt mycorrhizal network with some degree of soil continuity.

The species favours dry to mesic sclerophyll woodland and open forest on well-drained, acidic, often sandy or sandy-loam soils - the kind of terrain that characterises much of the inland southern and eastern Australian eucalypt belt.

Because the fruiting bodies are underground, you rarely see them without actively looking: probe the soil surface with fingers in likely spots, or look for the slight ground disturbance left by bandicoots, bettongs, and other small mammals that forage for native truffles and are important spore dispersers for the species.

The main fruiting period falls in Southern Hemisphere autumn and early winter - March through July - peaking in April and May.

The season is driven by the interplay of cooling soil temperatures and the re-wetting of soils after the long summer dry: as the first significant autumn rains penetrate the soil and temperatures drop below roughly 16 °C, ectomycorrhizal fungi throughout the eucalypt understory begin producing fruiting bodies.

Mesophellia glauca's hypogeous strategy means it does not need a surface rain event to push a cap through the soil; instead it completes development underground, and fruiting bodies can persist in reasonable condition for several weeks even after the initial moisture pulse.

Elevation and latitude shift timing: in cooler upland sites, March may see first fruiting; in warmer coastal zones May or June are more typical.

Solitary or in loose groups of two to five fruiting bodies, never densely clustered.

As an obligate mycorrhizal species, it regenerates in the same patches of forest from season to season, provided the host trees and undisturbed soil are intact.

The underground habit is an evolutionary strategy shared by several unrelated Australian fungi. It likely evolved as an adaptation to dry summers, allowing spore development in a protected, relatively humid microenvironment beneath the soil surface when the surface is too dry to support conventional above-ground fruiting.

Spore dispersal depends on soil fauna: bandicoots, bettongs, potoroos, and other small mammals excavate and eat hypogeous fungi, passing spores through their digestive systems and depositing them in new locations. This animal-fungus relationship is ecologically significant in Australian ecosystems.

Fruiting in Southern Hemisphere autumn (March-July) once soils cool below approximately 16 °C and receive at least 20 mm of rain in the preceding two weeks. As a hypogeous fungus developing entirely below the soil surface, flush lag is longer than for above-ground species - fruiting bodies may take 14-28 days to develop to detectable size after a triggering rain event. Bodies persist underground for several weeks, so a single rain trigger can support extended detectability.

Several groups of hypogeous or near-hypogeous fungi may be confused with Mesophellia glauca in Australian eucalypt forest.

• Scleroderma species (earthballs): round to irregular fruiting bodies at or just below the soil surface, often with a thick, warty peridium that is distinctly yellow-brown or ochre and a mottled or marbled grey-black interior gleba that smells strongly and pungently of old gas or rubber. They are poisonous (gastrointestinal irritants) and should not be confused with Mesophellia: the thick, tough, often cracked yellowish skin and the hard marbled interior are reliable separators.
• Pisolithus (horse dung fungus): irregular, brown-walled fruiting bodies with a distinctive layered or 'coffee-bean' interior of separate peridioles in a gel matrix - unmistakable in cross section.
• True Lycoperdon (puffball) species: typically sit above the soil surface, have a stem or sterile base, and white interior that does not become olive-powdery before the whole peridium ruptures at a pore.
• Labyrinthomyces and Castoreum: other native hypogeous truffles in the region, differing in spore morphology and internal structure.

At the field level, all native Australian hypogeous fungi should be treated as inedible unless specific edibility is firmly established.

Mesophellia glauca should not be collected for eating. It is classified as inedible: mature specimens are filled with a dry, powdery or waxy spore mass with an unpleasant earthy-to-musty odour and no culinary value; young specimens, while less developed, have no established tradition of preparation or any documented food use.

Collecting it out of curiosity for identification purposes is reasonable - probe the soil around the base of eucalypts in autumn, especially in spots where the ground shows signs of animal digging.

When examining a specimen:

• Note the glaucous bloom on the peridium.
• Confirm the underground habitat and eucalypt association.
• Check the interior colour and texture.

Photograph in situ if possible before removing, as habitat context aids identification.

Mesophellia glauca is not documented as toxic, and there are no confirmed reports of poisoning from this species.

However, it is also not edible in any established culinary sense: the mature gleba is a dry spore mass with no palatability, and young specimens have never been validated as food. The appropriate classification is inedible - not harmful, but not food.

The primary safety concern in the field is misidentification: Scleroderma species, which are genuine gastrointestinal toxins, can share the same habitat and superficially similar size and external appearance.

Always examine the peridium and the interior:

• Peridium: a smooth glaucous skin in Mesophellia versus a thick, warty, yellowish-brown skin in Scleroderma.
• Interior: olive-powdery maturing gleba in Mesophellia versus a hard marbled grey-black interior in Scleroderma.

When in doubt, do not eat any hypogeous fungus found in Australian eucalypt forest.