Star-spored Fibrecap

Star-spored Fibrecap is one of the best marked members of the nodulose-spored group of Inocybe, in which the spores bear pronounced angular knobs instead of being smooth. In this species the knobs are so long and pointed that a spore in profile looks like a child's drawing of a star, which is both the origin of the epithet asterospora and a decisive confirmation under any reasonable microscope.

In the field the species is recognised by a rich chestnut to date-brown cap that develops a strong central point and splits radially and deeply as it expands, together with a base of the stipe swollen into a distinctly rimmed, marginate bulb resembling a small flattened turnip. That combination of dark radially cracked cap and abruptly bordered bulb narrows the field considerably.

It is a woodland fungus of heavier soils, most often found on clay under broadleaf trees, and it fruits scattered along shaded banks and path sides through the second half of the year.

Cap

2–5 cm across, at first conical and then expanding to broadly convex with a strong, often sharply pointed umbo. The colour is chestnut, date-brown or reddish-brown, sometimes paler tawny toward the margin. The surface is dry and coarsely radially fibrillose, breaking into deep splits and slightly upturned fibre bundles as it expands, occasionally exposing the pale flesh beneath.

Gills

Adnexed, crowded, whitish to pale grey when young, ageing through clay to greyish or olive-brown. The edges are white and finely fringed, standing out clearly against the darker faces of mature gills.

Stipe

3–8 cm tall and 3–8 mm thick, roughly cylindrical but ending in a conspicuous marginate bulb, that is, a swollen base with a sharp rim or ledge around its upper edge. The stipe is pale brown to reddish-brown, and characteristically pruinose or finely mealy along its entire length rather than just at the apex. There is no ring.

Flesh and spore print

Flesh is whitish to pale brown and does not change appreciably when cut. The odour is faintly spermatic to earthy. The spore print is dull brown. Microscopically the spores are strikingly stellate, with roughly eight to twelve long conical projections, unmistakable in the genus.

Star-spored Fibrecap grows from soil in broadleaf and mixed woodland, showing a marked preference for heavy clay and loamy calcareous ground. It is found under beech, oak, hazel, hornbeam and lime, and also occurs in mixed plantings and old parkland with mature broadleaf trees. Path edges, shaded banks, ditch sides and eroded slopes where mineral soil is exposed are favourite spots.

Fruitbodies appear singly or in small scattered groups from summer to late autumn. The species is widespread but seldom abundant across Europe and temperate North America, and where the soil suits it may reappear in the same place for many years.

This is an ectomycorrhizal fungus that partners chiefly with broadleaf trees, especially beech, oak and hazel. Its hyphae form a mantle around the host's short roots, penetrating between the epidermal cells to create the network through which mineral nutrients are transferred to the tree and photosynthetic sugars flow back to the fungus.

The marginate bulb at the base of the stipe sits within the mycorrhizal mat in the upper soil, and fruitbodies often emerge from crumbling clay on bank faces where roots run close to the surface. The heavily ornamented spores may aid dispersal by clinging to the bodies of passing invertebrates in addition to being carried on air currents.

Inocybe rimosa is paler straw-ochre and lacks a marginate bulb, its stipe simply tapering or slightly swollen at the base and pruinose only near the apex. Inocybe maculata has a similar dark cap but retains whitish felted veil patches on the umbo and again has no rimmed bulb.

Other nodulose-spored fibrecaps such as Inocybe napipes, which has a turnip-shaped but less sharply rimmed base and a smoother, less split cap, and Inocybe praetervisa, which is yellower with a strongly marginate bulb, are best separated by spore shape under a microscope. Hebeloma species are altogether smoother-capped, slightly greasy when moist, and have sinuate gills with beaded edges.