Dingy Twiglet

The Dingy Twiglet (Simocybe centunculus) is the most frequently encountered member of the small genus Simocybe, a group of dark, dull-coloured wood-inhabiting gilled fungi related to Crepidotus and the fibrecaps in the family Crepidotaceae/Inocybaceae. The English name is apt: the fruit bodies are genuinely drab, in muted olive, khaki and umber shades that blend into the wet bark on which they grow.

Despite the modest appearance, Simocybe has a distinctive combination of characters. The cap surface is covered in a fine velvety or frosted bloom (a pruina) when fresh, giving it a soft matt look quite unlike the greasy or scurfy caps of similar-sized wood fungi. The gill edges carry a whitish frosting of sterile cells that shows clearly under a hand lens, and the top of the stem is dusted with the same pale bloom.

Because it is small, dark and undistinguished at a glance, the Dingy Twiglet is often passed over on fungus forays or lumped in with brown mushrooms generally. Once the velvety cap, olive tones and pale gill edging are recognised, however, it becomes a fairly recognisable feature of damp broadleaved woodland.

Cap

The cap is 1–3 cm across, at first convex or bell-shaped and expanding to broadly convex or almost flat, sometimes with a low broad umbo. The colour is a dull olive-brown, khaki, or dark umber, often paler and more ochre toward the margin, and it fades noticeably as it dries. The surface is matt and finely velvety or minutely granular-pruinose when young, with the bloom often wearing away in older specimens to leave a smoother, slightly wrinkled or veined disc. The margin may be faintly striate when moist.

Gills

The gills are adnate to broadly adnate, sometimes with a shallow notch, and are moderately spaced. They start pale clay or dull buff and darken to olive-brown or snuff brown as spores mature. A key feature visible with a lens is the gill edge, which is finely white-frosted or pruinose and contrasts with the darker gill face.

Stipe

The stipe is 2–4 cm long and only 2–4 mm thick, cylindrical, often curved where it emerges sideways from a branch. It is coloured much like the cap — olive-brown to dull ochre-brown, usually paler at the apex and darker toward the base — and is conspicuously pruinose or mealy in the upper part. There is no ring and no volva, and the base may carry a few pale mycelial fibrils binding it to the wood.

Flesh & spore print

The flesh is thin, pale brownish and unchanging when cut; there is no bruising reaction. The spore print is olive-brown to snuff brown. Microscopically the spores are smooth and ellipsoid to somewhat bean-shaped, and the cap surface bears distinctive rounded terminal cells that create the velvety bloom.

The Dingy Twiglet fruits on dead wood of broadleaved trees, typically on fallen branches, twigs and small logs lying on the woodland floor, and less often on standing dead limbs or old stumps. Recorded hosts include beech, oak, ash, hazel, elm, willow and sycamore. It favours damp, shaded, humus-rich deciduous woodland and shady hedge banks, and often fruits singly or in small scattered groups rather than dense clusters.

The main season runs from summer into autumn, with fruiting closely tied to spells of wet weather. The species is widespread and reasonably common throughout Europe, and Simocybe species with the same general appearance occur in North America and elsewhere in the temperate northern hemisphere.

Simocybe centunculus is a saprotroph and takes no part in mycorrhizal partnerships. Its mycelium colonises the outer wood and bark of dead broadleaved branches, causing a white rot in which lignin as well as cellulose is broken down, leaving the wood pale, soft and eventually fibrous. It is characteristic of the mid stages of branch decay, arriving after bark-inhabiting crusts and before the wood becomes fully crumbly.

Fruiting is opportunistic: a colonised branch may produce nothing for long dry periods, then push out a scatter of small caps within days of heavy rain. The short-lived fruit bodies release olive-brown spores that are carried on air currents to other fallen wood, and the fungus persists through unfavourable periods as mycelium within the branch.

Tubaria furfuracea, the Scurfy Twiglet, occupies similar habitats but has a distinctly hygrophanous tawny to date-brown cap with scurfy veil remnants along the margin rather than a velvety bloom, more widely spaced decurrent-toothed gills and an ochre-brown to rusty spore deposit. Other Simocybe species such as S. sumptuosa are close relatives separated mainly by larger size, darker colours and microscopic detail.

Psathyrella species growing on the same fallen wood are far more fragile, with markedly striate, hygrophanous caps, brittle hollow white stems and a dark grey-brown to blackish spore print. Crepidotus species share the wood substrate but have little or no stipe and fan-shaped laterally attached caps. Small Gymnopilus and Pholiota species are brighter tawny to rusty-yellow, often scaly rather than velvety, and Gymnopilus leaves a distinctly rusty-orange spore print rather than an olive-brown one.