Stalked Puffball-in-Aspic

The Stalked Puffball-in-Aspic is one of the most vividly coloured small fungi of eastern North American woodland. The fertile head is a bright cinnabar-red ball 1-2 cm across, sealed at the apex by four to six raised red lips arranged in a star. When young, the entire head is buried in a thick, clear, gelatinous coat that slowly sloughs off in glassy lumps, revealing the red sphere beneath.

Despite its puffball-like construction, Calostoma is not closely related to the true puffballs of the Agaricaceae. It sits in the Boletales, in the group that also contains the earthballs and the false truffles, and this relationship is reflected in its ecology rather than its shape.

The stalk is equally distinctive: rather than a solid woody column it is a spongy, open lattice of tangled gelatinous cords, reddish-brown to ochre, that holds the head 2-5 cm above the soil surface. Between the jelly, the red lips and the mesh-like stalk, the species is essentially unmistakable.

Head (spore case)

Globose to slightly flattened, 1-2 cm across. In young specimens it is enclosed in a thick, transparent to translucent gelatinous layer that falls away in clear jelly-like lumps, sometimes hanging in shreds around the stalk apex. The exposed spore case is bright cinnabar-red to orange-red, ageing to dull orange, ochre or brownish as pigment fades.

Mouth

The apex bears four to six raised, ridge-like lips arranged in a star or cross, coloured a deeper red than the case and remaining conspicuous even on faded specimens. Spores escape through the slit between them.

Stipe

2-5 cm tall, made of loosely tangled, gelatinous to cartilaginous cords forming a spongy, open, almost latticed column. It is reddish-brown, ochre or dull yellowish, and is usually partly buried in the substrate with soil and moss clinging to it.

Flesh and spore mass

The interior matures into a whitish to pale yellowish powder, unusually pale for a stalked gasteroid fungus, and the spores are elongate and finely pitted under magnification. Spores in mass are pale yellowish to whitish.

Grows on bare or thinly mossy soil, especially compacted clay: roadside cuttings, eroded stream banks, the sides of woodland trails, and steep exposed banks in mixed hardwood forest. It is strongly associated with oak and also occurs with other broadleaf trees and in oak-pine woodland.

The species is common in eastern North America, particularly the Appalachians and the southeastern states, extending north into New England and the Great Lakes region, and it is also known from Mexico, Central America and eastern Asia. Fruiting runs through the warm and humid months from summer into autumn, often in groups scattered along a single bank.

Unlike almost all other puffball-shaped fungi, Calostoma cinnabarinum is ectomycorrhizal. Its mycelium sheathes the fine root tips of oaks and other broadleaf trees, exchanging water and mineral nutrients drawn from the soil for sugars from the host. This partnership explains why the fungus is tied to particular forest types rather than to dead organic matter, and why it appears on eroded banks where tree roots are close to the surface.

The gelatinous layers are thought to be a moisture-retention device that lets the developing head survive on exposed, sun-warmed clay. Spore release is passive, spores drifting out through the starry mouth as the case dries and is jostled by rain.

Calostoma lutescens has a yellow to ochre head with a red star at the apex and, most distinctively, a conspicuous flared collar or rim of tissue at the base of the head where the outer layer remains attached; its stalk is longer and coarser. Calostoma ravenelii lacks the thick clear jelly, having instead a dull yellow-brown, mealy to granular head, though it too has reddish lips at the mouth.

True Lycoperdon puffballs are dry, dull-coloured and spiny or warty, with a plain circular apical pore and no gelatinous layer or lipped mouth. Small earthstars have a peeled-back star of rays at the base of the spore sac rather than a star of raised lips at the top of it.