American Matsutake

The American Matsutake belongs to Tricholoma, a large genus of ectomycorrhizal, white-spored, fleshy woodland fungi in the family Tricholomataceae, characterised by notched or sinuate gill attachment and stout stature. Within the genus it sits in the matsutake group, a small cluster of robust, aromatic, veiled species distributed around the Northern Hemisphere alongside the Japanese Tricholoma matsutake.

North American material has had a complicated naming history. Tricholoma magnivelare was described from eastern North America, while genetic work later separated the abundant western populations of the Pacific Northwest and California as Tricholoma murrillianum, with a further southwestern species, T. mesoamericanum, recognised in Mexico and Central America. Field guides and common usage still often apply the older name across the continent, and the field characters described here apply to the group as a whole.

What makes it distinctive is a combination that no other white Tricholoma quite matches: dense, heavy, almost solid flesh; a dry white surface that develops rusty cinnamon fibrils and stains; a thick cottony sheathing ring; and above all a penetrating aromatic odour, variously described as spicy, cinnamon-like or resinous. Fruiting bodies push up slowly through packed sand and needle duff, often lifting a cap of litter and remaining half-buried, so experienced observers look for the tell-tale mound rather than the mushroom.

Cap

5-20 cm across, occasionally much larger, at first a firm white dome with a strongly inrolled margin, then convex and finally broadly flat. The surface is dry and silky to slightly fibrillose, pure white when young, and progressively develops flattened cinnamon, tan or reddish-brown fibrillose patches and stains, especially over the centre and wherever the cap has been touched or has pushed against litter. Old caps can be extensively brown-stained over a white ground.

Gills

Sinuate, that is notched where they meet the stem, crowded, fairly narrow, white to cream, and bruising and ageing to reddish-brown or rusty spots. Gills are covered in young specimens by a thick white partial veil that stretches from the cap margin to the stem.

Stipe

5-15 cm tall and 2-4 cm thick, extremely firm and solid, cylindrical or tapering to a narrowed base that is often deeply buried in sand. Above the ring it is white, smooth and finely floury; below the ring it is covered with the same brownish fibrillose scaling and staining as the cap. The ring itself is distinctive: thick, cottony and membranous, forming a flaring sheath around the upper stem rather than a thin skirt.

Flesh & spore print

Flesh is white, thick, dense and unchanging or slowly staining brownish where cut. The odour is strong, aromatic and spicy, sometimes likened to cinnamon mixed with resin, and is detectable from a short distance in a good fruiting. The spore print is white and the spores are smooth and broadly ellipsoid.

This is a fungus of sandy, well-drained, nutrient-poor conifer ground. In the west it fruits abundantly under lodgepole and shore pine, western hemlock, Douglas fir and true firs, and in mixed stands with tanoak and madrone; in the east it is associated with jack pine, red pine, eastern hemlock and spruce, often on sandy glacial soils and coastal dunes. It usually appears where the duff layer is deep and the mineral soil sandy, frequently on slopes and ridges.

Fruiting begins in late summer at higher elevations and inland, continues through autumn, and can persist into December and January in mild coastal areas of the Pacific Northwest and California. Fruiting bodies commonly emerge only partly above the surface, lifting a hummock of needles and moss, and often occur in rings, arcs or dense troops radiating from an underground mycelial mat.

The American Matsutake is ectomycorrhizal. Its hyphae wrap the fine root tips of conifers in a dense sheath and grow between the outer root cells, forming an interface across which the fungus supplies water, nitrogen and phosphorus drawn from a large volume of soil in exchange for sugars from the tree. This partnership is essential to the nutrition of pines and hemlocks on the poor sandy soils where the species thrives.

The mycelium builds a characteristic structure known in Japanese as a shiro: a dense, whitish, more or less circular mat of mycelium and colonised roots that expands outward through the duff and mineral soil by several centimetres a year. The mat compacts the soil, excludes many competing fungi and roots, and produces fruiting bodies around its advancing edge, which is why arcs and rings are so typical. A shiro can persist and expand for decades, tying the fungus tightly to the longevity of its host stand, and it is highly sensitive to disturbance of the duff layer.

Amanita smithiana is the classic confusion in western conifer forests, and is separated by having free gills rather than notched ones, a soft powdery or shaggy universal veil rather than a thick sheathing ring, an abruptly enlarged or spindle-shaped rooting stem base, and no spicy aroma. Amanita silvicola similarly has free gills and a soft cottony universal veil.

Catathelasma ventricosum shares the dense white flesh and conifer habitat but has decurrent gills running down the stem, a double ring, and a stem that tapers to a sharp rooting point. Tricholoma focale is genuinely related and shares the notched gills and ring, but its cap is orange-brown to brick and its ring is a conspicuous banded girdle of orange fibrils. Ordinary white Tricholoma species such as T. columbetta lack any ring at all and lack the aroma.