Deadly Webcap

Cortinarius rubellus, formerly known as C. speciosissimus and C. orellanoides, belongs to the section Orellani, a small group of tawny to foxy-brown webcaps of northern and upland forests. It is a comparatively slender fungus with a distinctly conical, sharply pointed cap that stays prominent even after the rest of the cap has flattened around it.

Cortinarius is the largest genus of gilled fungi in the world, with well over two thousand described species, all of them united by a cobweb-like partial veil called a cortina that stretches from the cap margin to the stem in young specimens and by a rusty brown spore print. As the cap expands the cortina tears, and the falling rusty spores stain the collapsed threads, leaving a rusty fibrous band on the stem that is often the clearest evidence that a mushroom belongs to this genus.

Within that vast genus, section Orellani is recognised by dry, finely fibrillose to scurfy caps in warm foxy orange-brown tones, thick and comparatively widely spaced gills, and yellowish flesh. C. rubellus is the boreal, conifer-associated member, and it is one of a relatively small number of Cortinarius species that can be named with confidence in the field on macroscopic characters alone.

Cap

The cap is 3-8 cm across, conical to bell-shaped when young and expanding to broadly convex while retaining a sharp, narrow, distinctly pointed umbo at the centre. The surface is dry and matt, covered in fine radial fibrils that break into minute scurfy scales, especially over the disc. The colour is a warm tawny orange-brown, foxy red-brown, or coppery, usually a little darker over the umbo.

Gills

The gills are adnate to narrowly attached, thick, rather broad, and noticeably distant compared with most gilled fungi of similar size. They begin a warm ochre to saffron brown and darken to rusty cinnamon brown as the spores ripen. The gill edges may be slightly paler and uneven.

Stipe

The stipe is 5-12 cm long and 0.5-1.5 cm thick, slender, often slightly club-shaped or tapering downwards, and coloured tawny yellow-brown. Its most useful feature is the presence of one to several irregular pale yellow to lemon-yellow fibrous girdles or bands encircling the stem, the remains of a yellowish universal veil. Above these sits the rusty fibrillose zone left by the cortina. There is no membranous ring and no volva.

Flesh and spore print

The flesh is firm, pale ochre-yellow to yellow-brown, and does not stain strongly when cut. The odour is faint and has been likened to radish. The spore print is rusty brown, matching the mature gills.

This is a fungus of damp, acidic conifer forest, most typically under Norway spruce and Scots pine, and it is closely associated with a ground layer of Sphagnum and other mosses, bilberry, and heather. It favours cool, humid, often upland or boreal sites, including bogs, wet forest hollows, and mossy plantation floors, and it is much less frequent on dry or base-rich soils.

The distribution is northern: it is widespread in Scandinavia, Scotland and the uplands of Britain, the Alps and other European mountain ranges, and across northern Asia and northern North America. It fruits singly or in small scattered groups from late summer into autumn, with numbers rising sharply after prolonged wet weather.

Cortinarius rubellus is ectomycorrhizal. Its mycelium forms a sheath around the fine feeder roots of conifers, principally spruce and pine, and grows between the outer root cells to create the exchange interface known as the Hartig net. Through this the fungus supplies the tree with water, phosphorus, and nitrogen scavenged from the acidic and often nutrient-poor forest soil, and receives sugars produced by photosynthesis in return.

Because the relationship is obligate, the fungus cannot be grown away from a host and it appears only where suitable conifers are established. Its preference for wet, mossy, acid ground makes it part of the characteristic fungal community of boreal and montane forest, alongside other Cortinarius species, Russula, Lactarius, and Suillus. The cortina protects the young gills during development, and the rusty spores it releases in autumn are dispersed by air movement through the open forest floor.

Cortinarius orellanus is the closest relative and is separated by cap shape and stem markings: its cap is convex to broadly flattened without the sharp pointed umbo, and its stem is plain yellowish and lacks the distinct pale yellow encircling bands. The two also differ in habitat, C. orellanus growing with broadleaf trees, especially oak and beech, on warmer soils, while C. rubellus is a conifer and Sphagnum species of cooler regions.

Several other tawny webcaps overlap in colour. Members of the Cortinarius cinnamomeus group are smaller and slimmer with more crowded gills in brighter cinnamon to yellow tones and no yellow stem girdles. The Chanterelle, Cantharellus cibarius, is sometimes compared on colour alone but is structurally quite different: it has blunt, forking, decurrent ridges instead of true blade-like gills, a paler egg-yellow colour throughout, a white spore print, and no cortina at any stage. Gymnopilus species also give rusty spore prints but grow in clusters on wood rather than singly from mossy soil.