Wine Cap

Stropharia rugosoannulata is the giant of its genus, capable of producing caps thirty centimetres across in a rich wood-chip bed. It is a fungus of made ground rather than wild woodland, and it has spread widely through gardens, parks, and landscaped areas wherever bark and wood chip mulch is used, often arriving with the mulch itself.

The genus Stropharia belongs to the family Strophariaceae and is defined by attached gills, dark purple-brown to purple-black spore prints, and a well-developed membranous ring. What makes this species instantly recognisable is the structure of that ring: the epithet rugosoannulata means wrinkled-ringed, and the thick upper surface of the ring is grooved into radiating ribs that break into pointed segments, producing a shape usually described as a cogwheel or star.

Colour is variable and can mislead. Young caps in cool damp conditions are a deep wine red or burgundy, but sun and age bleach them through reddish tan to buff, dull ochre, and finally a washed-out greyish straw, so a single bed can show several apparently different mushrooms at once.

Cap

The cap is 5-20 cm across and sometimes far larger, hemispherical and tightly domed when young with the margin curled under, then convex and finally broadly flattened, occasionally with a shallow central depression in age. The surface is dry and smooth, sometimes finely cracked in dry weather, and the margin often retains white triangular fragments of the partial veil. Colour runs from deep wine red or reddish purple-brown when young through reddish tan to buff, straw, or greyish ochre as it weathers.

Gills

The gills are adnate, crowded, and moderately broad. They start pale whitish grey, pass through a distinctive pale lilac or violet-grey stage, and finish dark purple-brown to almost blackish purple as the spores mature. Gill edges are often finely white-fringed and paler than the faces.

Stipe

The stipe is 8-15 cm long and 1-3 cm thick, stout, solid, white to cream, and smooth above the ring with a slightly scurfy or scaly texture below in some collections. It is usually somewhat swollen or club-shaped at the base, from which thick white mycelial cords, or rhizomorphs, radiate into the substrate. The ring is the diagnostic feature: thick, membranous, positioned high on the stem, and grooved on its upper surface into radiating ribs that split into star-like points, frequently stained dark by fallen spores.

Flesh and spore print

The flesh is thick, firm, and white, showing little or no colour change when cut, with a mild earthy odour. The spore print is dark purple-brown to purple-black.

This is a species of rich, disturbed, woody or strawy substrates rather than undisturbed forest soil. It fruits abundantly in hardwood chip and bark mulch on garden beds, path edges, playgrounds, and municipal landscaping, and also on straw, sawdust, composted plant waste, and heavily enriched garden soil. Fruiting typically begins a few months after fresh mulch is laid and can continue for two or three seasons until the substrate is exhausted.

The season is long, running from late spring through summer and into autumn, with flushes following heavy rain and warm weather. It is native to temperate Europe, Asia, and North America and is now effectively cosmopolitan in temperate regions, its distribution greatly extended by the international trade in mulch and by deliberate establishment in wood-chip beds.

Stropharia rugosoannulata is a saprotroph and an aggressive coloniser of coarse woody debris. Its mycelium forms conspicuous thick white cords that run through chip and straw beds, and it breaks down lignin and cellulose in a white-rot process, converting rough mulch into dark crumbly humus. It competes strongly with other decomposers and can dominate a fresh bed within a single season.

The fungus is unusual in preying on nematodes. Its mycelium produces specialised acanthocyte cells, spiny star-shaped structures that immobilise and puncture soil nematodes, allowing the fungus to draw nitrogen from them and supplement what is a nitrogen-poor wood diet. These acanthocytes are also a definitive microscopic character for the genus. Ecologically the species is an important recycler in landscaped ground, improving soil structure and speeding the turnover of woody waste.

Other Stropharia species share the purple-brown spore print and ring, but none has the cogwheel ring. Stropharia hornemannii is a conifer-wood species with a distinctly viscid, glutinous cap in purplish brown, and a smooth ring. Stropharia aeruginosa is small and unmistakably blue-green with a slimy cap. Stropharia coronilla is much smaller, yellow-buff, and grows in grassland, with a smooth ring.

Large Agaricus species can approach it in size and stature but have gills completely free of the stem that pass through a clear pink stage to chocolate brown, and give a dark brown rather than purple-black spore print; their rings are smooth or split into a cogwheel on the underside rather than grooved on top. Agrocybe species growing in the same mulch beds are smaller and drop dull tobacco-brown spores. Hypholoma species also give purple-brown prints but are much smaller, cluster tightly on wood, and leave only a cobwebby ring zone rather than a thick membranous ring.