Tricholoma ustale (Fr.) P. Kumm. - Burnt Knight

Phylum: Basidiomycota - Class: Agaricomycetes - Order: Agaricales - Family: Tricholomataceae

Tricholoma ustale, Burnt Knight

One of the more common of the brown-capped Tricholoma species, the Burnt Knight is easily overlooked because its cap blends in so well against a background of fallen Beech leaves. It is mycorrhizal with broadleaf trees, notably Beeches and Hornbeams, where it usually occurs in small groups.

Distribution

The Burnt Knight mushroom is a fairly frequent find throughout Britain and in Ireland, most commonly in Beech woodland (and therefore very often on alkaline soil.

Tricholoma ustale is found throughout most of mainland Europe; a species by the same name is also found in parts of North America.

Tricholoma ustale, Burnt Knight, young specimens

Taxonomic history

This mushroom was first described scientifically in 1818 by the great Swedish mycologist Elias Magnus Fries, who named it Agaricus virgatus. (Most of the gilled mushrooms were included initially in the genus Agaricus, which has since been slimmed down considerably as many other new general have been created to house most of its former residents.)

German mycologist Paul Kummer transferred this and several other 'knights' to the genus Tricholoma in 1871.

Synonyms of Tricholoma ustale include Agaricus ustalis Fr., Agaricus fulvellus Fr., and Tricholoma fulvellum (Fr.) Gillet.

Etymology

Tricholoma was established as a genus by the great Swedish mycologist Elias Magnus Fries. The generic name comes from Greek words meaning 'hairy fringe', and it must be one of the least appropriate mycological genus names, because very few species within this genus have hairy or even shaggily scaly cap margins that would justify the descriptive term. The specific epithet ustale comes from the Latin adjective ustalis and means burnt - a reference to the colour of the cap if this mushroom.

Identification guide

Cap of Tricholoma ustale

Cap

A lovely chestnut brown, pale at the margin and darker at the centre and often blackening with age, convex, flattening but usually retaining a broad umbo;surface smooth and very viscid in wet weather; 4 to 8cm across when fully expanded.

Pileipellis of Tricholoma ustale

Pileipellis

Up to 250µm thick, comprising hyphae mainly in the range 2.5 to 6.5µm in diameter, with noticeable banded incrustations (see left).

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Gills of Tricholoma ustale - Burnt Knight

Gills

Pale creamy grey, developing rusty brown spots with age; crowded; sinuate or emarginate.

Stem

White and fibrous, lined longitudinally with brown fibrils, somewhat darker towards the base; cylindrical or slightly clavate; 3 to 6cm long, 1 to 1.5cm diameter; no ring. The stem flesh is white, turning reddish brown when cut or bruised.

Spore of Tricholoma ustale

Spores

Broadly ellipsoidal, smooth, 6-7.5 x 5-6µm, with a noticeable hilum; inamyloid.

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Spore print

White

Odour/taste

Odour not significant; taste slightly bitter.

Habitat & Ecological role

Ectomycorrhizal with broadleaf trees, particularly Beech but also oaks, birches and occasionally even limes and Hawthorn.

Season

Late summer and autumn in Britain and Ireland.

Similar species

Tricholoma fulvum occurs in wet grassland under birches.

Tricholoma ustuloides is much rarer (in Britain) and has a distinct white region at the stem apex.

Culinary Notes

Tricholoma ustale is not recommended as an edible mushroom as some authorities state that it is a poisonous species.

Tricholoma ustale, Carmarthenshire, Wales

Reference Sources

Fascinated by Fungi, Pat O'Reilly 2016.

Kibby, G (2013) The Genus Tricholoma in Britain, published by Geoffrey Kibby

BMS List of English Names for Fungi

Dictionary of the Fungi; Paul M. Kirk, Paul F. Cannon, David W. Minter and J. A. Stalpers; CABI, 2008

Taxonomic history and synonym information on these pages is drawn from many sources but in particular from the British Mycological Society's GB Checklist of Fungi and (for basidiomycetes) on Kew's Checklist of the British & Irish Basidiomycota.

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