Tricholoma fulvum

What You Should Know

Tricholoma fulvum is an inedible mushroom with a strongly farinaceous odor when cut. This fungus habitat in small groups, ectomycorrhizal, in association with Betula, in swamp forest, and dry deciduous woods. The caps expand with a low central umbo, mature caps are radially streaky.

This mushroom occurs in large numbers on wet woodland edges, but also keeps an eye open for these atypical knights where birches have sprung up as pioneer trees on the disturbed boggy land beside low-lying forestry tracks.

Most of the Tricholoma fungi (the 'knights') have white gills, but this is an exception and with its tendency to develop brown spots on its gills plus the distinctive cap striations the Tricholoma fulvum is arguably the most distinctive member of this tricky group of mushrooms.

Other names: Birch Knight, Yellowbrown Knight Cap, Birke-ridderhat (Danish), Berkenridderzwam (Dutch), Tricolome brun et jaune (French), Gelbblätriger Ritterling (German).

Tricholoma fulvum Mushroom Identification

1. Cap

   3-15 cm diameter, convex with an umbo and involute to deflexed margin initially, expanding to applanate with or without low umbo, sometimes with undulating marginal zone, with straight margin, red-brown with paler marginal zone, subviscid when moist, becoming distinctly radially fibrillose on drying, finally often breaking up in small, irregular, appressed squamules; marginal zone often having a rough rib-like texture with age.

2. Gills

   Crowded, adnate–emarginate, occasionally forked near the attachment of stem, narrowly ventricose, pale yellow, often developing reddish-brown spots on edges in maturity, with an eroded, concolorous edge, particularly near the edge when old.

3. Stem

   4-12 cm tall x 0.5-2 cm thick, cylindrical, sometimes tapering upwards, sometimes flexuous, at very apex white, finely pruinose-flocculose, sometimes rather sharply delimited from lower part; below strongly fibrillose-subsquamulose with red-brown fibrils on paler, yellow or brown background, basal part often tinged clear yellow; becoming hollow with age.

4. Spore Print

   White.

5. Spores

   Subglobose to oblong with a pronounced hilar appendage, smooth, nonamyloid, 5-6.5 x 3.5-5 µm.

6. Similar Species

   Tricholoma equestre has a brown-yellow cap but is distinguished by its bright-yellow gills.

Tricholoma fulvum Taxonomy and Etymology

There has been much debate over the authority of the Birch Knight. Although this mushroom was described scientifically in 1792 by French mycologist Jean Baptiste Francois (Pierre) Bulliard, who named it Agaricus fulvus, its currently accepted binomial was established as recently as 1913, when French mycologists René Bigeard (1840 – 1917) and Henri Guillemin (biographical dates not known to us) transferred this species to the genus Tricholoma, establishing the binomial name as Tricholoma fulvum.

Synonyms of Tricholoma fulvum include Agaricus fulvus Bull., Agaricus flavobrunneus Fr., Agaricus nictitans Fr., Tricholoma flavobrunneum (Fr.) P. Kumm., and Tricholoma nictitans Fr.) Gillet.

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 fulvum comes from Latin and means tawny (yellowish-brown).

Sources:

Photo 1 - Author: Jörg Hempel (Creative Commons Attribution-Share Alike 3.0 Germany)

Photo 2 - Author: Jerzy Opioła (Creative Commons Attribution-Share Alike 3.0 Unported)

Photo 3 - Author: bjoerns (Creative Commons Attribution-Share Alike 4.0 International)

Photo 4 - Author: Thkgk (Creative Commons Attribution-Share Alike 3.0 Unported)