Hairy Earthtongue

The Hairy Earthtongue (Trichoglossum hirsutum) is an ascomycete, not a gilled fungus, and belongs to the Geoglossaceae — the earthtongues. Instead of a cap and gills it produces a simple upright club: a flattened, lance-shaped or tongue-shaped fertile head carried on a slender cylindrical stalk, the whole structure jet black and only a few centimetres tall.

The defining character of Trichoglossum is hairiness. The surface bears numerous projecting dark bristles called setae, thick-walled and pointed, which give the fruitbody a matt, velvety or minutely shaggy look and a slightly dusty appearance in raking light. Smooth-surfaced earthtongues in the genus Geoglossum look shiny or greasy by comparison, and the distinction between the two genera rests on these setae, best confirmed with a hand lens or microscope.

Earthtongues are among the most valued indicator fungi of unimproved grassland. Along with waxcaps, pinkgills and club fungi, their presence signals turf that has escaped ploughing, reseeding and heavy fertiliser for many decades, and they are used as a survey tool in grassland conservation.

Fruitbody

3 to 8 cm tall overall, occasionally taller in sheltered moss. The upper fertile part is a flattened, lance-shaped, tongue-like or narrowly club-shaped head, typically one third to one half of the total height, sometimes grooved or furrowed lengthwise when dry. It is black throughout.

Surface

The entire fruitbody, head and stalk alike, is covered in fine projecting black bristles, giving a matt, velvety, minutely hairy texture. Under a lens the surface looks finely spiny rather than smooth. The stalk is round in section, slender, sometimes slightly paler and roughened at the very base where it meets soil and moss.

Flesh & spores

The flesh is blackish and tough-fleshy rather than brittle. Spores are produced in asci on the fertile head; they are long, narrowly cylindrical to slightly curved, brown-black in mass, and characteristically divided by around fifteen cross-walls (septa) at maturity — a feature used to separate species within the genus. Setae are thick-walled, dark and tapering.

The Hairy Earthtongue grows among short mosses in unimproved, nutrient-poor grassland: old pasture, churchyards, lawns that have never been fertilised, upland hay meadows, coastal grassland, dune slacks and mossy woodland banks. It is very often found in the company of waxcaps and grassland Entoloma, and thrives where the moss layer is thick and the turf is short.

Fruiting is mainly from late summer into autumn, peaking in September and October, and the black fruitbodies are easily missed against dark moss. The species is widespread across Europe, North America and temperate Asia, but has declined in intensively farmed regions along with the grassland habitat it depends on.

Trichoglossum hirsutum is generally regarded as saprotrophic or possibly biotrophically associated with mosses and grassland plants; the precise nutritional strategy of the Geoglossaceae remains incompletely understood. What is clear is that it depends on stable, undisturbed, low-nutrient soil with an intact moss and organic layer, and it disappears rapidly where turf is ploughed, reseeded or fertilised.

As an ascomycete it releases spores actively: the asci lining the fertile head build up internal pressure and shoot the long multi-septate spores clear of the surface, where air currents carry them away. The upright tongue shape lifts this spore-shooting surface above the moss layer and out of the still air at ground level.

Geoglossum species are the closest look-alikes and are essentially identical in shape and colour, but they lack setae, so their surface appears smooth, shining or slightly greasy rather than matt and velvety. A hand lens on the stalk usually settles it, and a microscope confirms the presence or absence of bristles. Within Trichoglossum, T. walteri has spores with fewer septa, typically around seven, and T. rasum has a nearly smooth stalk.

Microglossum species share the club shape but are coloured — olive-green, yellow-green or purplish — and smooth. Xylaria hypoxylon, the Candlesnuff, is black at the base but branches into antler-like tips dusted white with powdery conidia, and grows on dead wood rather than in turf. Clavaria and Clavulinopsis clubs in the same grassland are brightly coloured or white and brittle, never black and velvety.