Winter Stalkball Identification Guide

First impressions and the setting

Winter Stalkball is small enough that most people walk over it for years before seeing one. The setting is highly specific and is the best search strategy you have: dry, base-rich, mossy ground. Fixed sand dunes with a mossy grey crust, the mortared tops of old walls, calcareous grassland on thin soil, sandy banks and the mossy margins of tracks over chalk or limestone are all classic places.

The first impression, once your eye adjusts, is of a miniature puffball on a stick. A pale spherical head five to ten millimetres across sits at the top of a thin, wiry, brownish stalk two to four centimetres tall, poking out of a cushion of moss. From above it can look like a tiny mushroom; from the side the structure is unmistakable, because a puffball on a slender woody stalk is a form that very few fungi adopt.

Once you find one you will usually find a dozen. They occur in loose colonies scattered through the same moss patch, and it pays to kneel and scan systematically.

Reading the spore head

The head is the fertile part and needs a hand lens.

Shape is globose to slightly flattened-globose, five to ten millimetres across, occasionally a little larger. The outer wall in fresh material is a thin, sandy, granular skin, often with sand grains and soil particles adhering, which flakes away to reveal the smooth inner wall beneath. That inner wall is pale: whitish, cream, buff or pale greyish-brown, thin and papery, and it darkens and dulls with weathering.

The mouth is the single most important character. At the apex of the head there is a distinct, raised, tubular or cylindrical opening - a small chimney or nipple projecting a fraction of a millimetre above the surface, with a neat circular aperture. Around that aperture is a narrow darker rim, brownish or blackish, sharply defined against the pale wall. Under a lens the whole structure reads as a small dark-lipped funnel set on the top of the ball.

Press a mature head gently and a puff of fine rusty-brown spore dust escapes from the mouth. That dust colour - warm ochre to rust or cinnamon brown, never olive, never purple - is worth noting.

The stalk and the socket

The stipe is two to four centimetres long and one to three millimetres thick, slender, more or less equal or slightly thicker at the base, and often curved or slightly twisted. It is tough and woody rather than fleshy, and it does not compress between the fingers.

Colour is pale brown, tan, ochre-brown or dull straw, darkening with age. The surface is finely scaly, fibrillose or shredded, with small recurved scales especially in the lower half, giving a slightly shaggy texture under a lens.

Where the stalk meets the head there is a small socket. The top of the stalk is inserted into a corresponding depression in the base of the spore ball, and with care the head can be lifted off to show the fitted joint. This socketed insertion is a genus character and separates the group from fungi where the stalk simply continues into the head.

The base of the stalk descends into the moss and sand and is usually wrapped in a mass of mycelium binding sand grains into a lumpy, gritty root-like plug. Excavate carefully with a knife or your fingers, because snapping the stalk loses this feature. There is no cup, no volva and no ring anywhere.

Flesh, spore mass and colour change

There is no fleshy tissue to speak of in a mature fruit body. Slice a head open and you find it packed with a dry, powdery spore mass, rusty brown to cinnamon, threaded through with fine capillitium fibres that give it a slightly cottony consistency.

Very young unopened heads are firmer and paler inside, whitish to yellowish, and gradually mature and dry from the inside out. Cut surfaces show no colour change, no bruising reaction and no latex. The stalk is solid to fibrous-stuffed and pale brown inside.

Spore print and microscopic notes

A conventional spore print is neither possible nor needed, because the fungus is a puffball relative that releases spores through the apical pore rather than dropping them from a hymenium. To sample the spores, tap a mature head over a sheet of white paper or a slide and you will collect a fine rusty-brown powder.

Under the microscope the spores are globose and distinctly ornamented, warted or finely spiny rather than smooth, and typically three to five micrometres in diameter. The capillitium threads are hyaline to pale, thick-walled and conspicuously swollen and thickened at the septa, which is a useful confirming feature within the genus.

Substrate and season

The fungus is a saprotroph of the soil and moss layer, decomposing organic matter in thin, dry, base-rich, well-drained substrates. The strong associations are with calcareous ground and with fixed dunes, and it is very often found growing directly among mosses such as the grey cushion mosses that crust stabilised sand, or in the mossy mortar of old walls, ruins and church boundaries.

The season explains the name. Fruit bodies mature in late autumn and persist through winter into early spring, and because the head and stalk are tough and dry rather than fleshy they weather well and can remain standing for months after maturity. Old, wind-scoured specimens with bleached heads are frequently found alongside fresh ones. In practice this means it is one of the very few fungi worth searching for on a bright cold day in midwinter.

Separating it from the look-alikes

Tulostoma melanocyclum is the closest problem. Its mouth is not raised into a clear tube in the same way, and it is surrounded by a broader, more diffuse dark zone or halo rather than a narrow crisp rim, and the stalk tends to be stouter and darker.

Tulostoma fimbriatum has a mouth that is not tubular at all but is a torn, fibrillose, fringed opening without a dark defined margin, and its outer wall persists longer as a scurfy coat.

Battarrea phalloides superficially shares the plan of a spore head on a stalk, but it is enormously larger, with a stalk that can reach several tens of centimetres, a shaggy woody stem and a distinct volva at ground level, and the spore mass is shed by the whole upper surface rather than through a small pore.

Lycoperdon and Bovista puffballs may have a sterile base that narrows downwards, but that base is soft, chambered and continuous with the head, not a thin woody stalk socketed into it, and there is no dark-rimmed tubular mouth.

Geastrum earthstars open by splitting the outer layer into rays that spread out beneath the spore sac; there is no true stalk and the star of rays is unmistakable.

Small stalked slime moulds in the same moss are far smaller, usually under five millimetres tall, and lack the tough scaly stipe and socketed head.

Quick field checklist

A small pale spore ball with a raised tubular mouth ringed in dark brown, socketed onto a slender, tough, finely scaly brown stalk, growing in moss on dry calcareous or dune sand, in colonies, in late autumn and winter, releasing rusty-brown spore dust when tapped.