Soapy Knight

The Soapy Knight is one of the most variable species in Tricholoma, a genus of fleshy, ringless, white-spored woodland mushrooms with sinuate or notched gills. Cap colour in this species ranges through olive-green, grey-green, dull yellow-green, sooty grey and even pale brown or almost white, and several varieties have been named on the basis of colour and scaliness alone.

What holds the species together as a recognisable unit is its texture and smell. The flesh is firm and slightly rubbery, and the fruit body carries a peculiar odour widely described as soapy or like household laundry soap, sometimes with a mealy undertone. This scent, combined with a tendency for the cut flesh to flush pink, is the standard way to confirm the species.

As a genus, Tricholoma is characterised by robust stature, gills that are notched where they meet the stipe, a white spore print and, in almost all species, an ectomycorrhizal partnership with forest trees.

Cap

The cap is 4-10 cm across, convex at first with an inrolled margin, later flat to broadly umbonate, often with a wavy or lobed margin. The surface is dry to slightly greasy when wet, smooth in some forms and finely cracked into small scales in others, and coloured olive-green, grey-green, sooty grey, drab yellow-green or pale brownish; the centre is usually darker than the margin.

Gills

The gills are notably widely spaced for the genus, fairly broad and sinuate, that is notched at the point where they meet the stipe. They are white to pale cream or with a faint greenish or yellowish tinge, and often become spotted or edged with pinkish or rusty marks where bruised or aged.

Stipe

The stipe is 5-10 cm long and 10-25 mm thick, cylindrical or tapering downwards to a somewhat rooting point, white to greyish and often flushed with green, grey or pinkish fibrils. It may be smooth or finely scaly. There is no ring and no volva.

Flesh and spore print

The flesh is firm, white and thick, and characteristically flushes pale pink to salmon-pink where cut or bruised, most obviously in the lower stipe and base. The smell is soapy, sometimes with a mealy or slightly fruity note. The spore print is white and the spores are smooth and elliptical.

The Soapy Knight grows on soil in both broadleaf and coniferous woodland, associating with beech, oak and birch as well as spruce, pine and fir. It occurs on a wide range of soils from acid sands to chalk and is often found along woodland tracks, on banks and in moss under mature trees.

Fruiting runs from late summer through autumn, usually solitary or in small scattered groups, occasionally in loose rings. It is widespread and common across Europe and temperate Asia and is recorded widely in North America, where a complex of closely related forms occurs.

Tricholoma saponaceum is ectomycorrhizal. Its mycelium forms a sheath around the fine roots of its host trees and a network of hyphae between the outer root cells, exchanging soil-derived water, nitrogen and phosphorus for sugars produced by the tree. This partnership explains its restriction to established woodland and its absence from open grassland.

Because it partners with both broadleaf and coniferous hosts, it is one of the more catholic members of the genus in its tree associations. The rooting stipe base is characteristic of mycorrhizal Tricholoma species, which anchor deeply into the soil where the root connection lies rather than sitting in the surface litter as saprotrophic funnels do.

Tricholoma sejunctum has a yellowish-green cap with dark radiating fibrils and a whiter stipe, and its flesh does not flush pink. Tricholoma portentosum is streaky grey with a violet or yellow tinge and a greasy cap, with gills that develop yellowish edges and flesh that stays white. Tricholoma terreum is smaller, dry and felty-grey without green tones and with no pink flush in the flesh.

Green-capped Russula species can resemble pale forms in colour but have brittle, crumbly flesh, gills that are adnate rather than notched, and a stipe that snaps like chalk. The reliable separators for the Soapy Knight are the widely spaced notched gills, the pink flush in cut flesh at the stipe base, the soapy smell and the white spore print.