Larch Bolete Identification Guide

The Tree Comes First

No larch, no Larch Bolete. Suillus grevillei is an obligate partner of Larix, and that single fact removes most of the identification problem before you touch the fungus. Larch is the deciduous conifer: soft needles in rosettes on short spurs, bright green in spring, gold in autumn, bare in winter, with small woody cones that persist on the twigs. Look for the tree, look for the cones underfoot, and only then look down at the mushroom.

Typical settings are larch plantations, mixed shelterbelts, park avenues and estate woodland. Fruitbodies come up in grass, moss and needle litter, often in numbers, sometimes in loose rows following a root, from late summer through to the first frosts.

First Impressions

Even at a distance the cap reads as lacquered. Suillus grevillei is one of the shiniest boletes: a smooth, domed, golden to chestnut cap with a wet gloss that reflects the sky. Caps run 4 to 12 cm, hemispherical at first, then convex, and finally broadly flattened with a low central rise.

Reading the Cap

Touch it and your fingers stick slightly. The surface carries a thin glutinous layer that is genuinely tacky in damp weather and merely shiny and varnished-looking when it dries. That layer peels away as a coherent skin if you lift an edge with a thumbnail, a useful confirmation of the slippery Suillus group.

Colour varies more than beginners expect within one stand: bright chrome-yellow and golden in some fruitbodies, orange-brown, tawny or deep chestnut in others, often with the centre darker and the margin paler and yellower. What does not vary is the smoothness, with no fibrous scales and no cracking.

The Pore Surface

Turn it over. Pores are small, round to slightly angular, and much finer than in the scaly Suillus species. Young ones are a clean lemon to chrome yellow, ageing dingy ochre and finally olive-brown. The tube layer is shallow, adnate to slightly decurrent, and does not separate cleanly from the cap flesh.

Press the surface. It stains slowly but distinctly rusty brown, ochre-brown or vinaceous where handled, and old fruitbodies are covered in brown thumbprints from earlier visitors. This slow brownish bruising, without any true blue, is characteristic.

Stipe, Ring and the Two-Tone Rule

The stipe is 4 to 10 cm long, 1 to 2 cm thick, cylindrical or slightly swollen below, solid and firm. The key is that it comes in two halves divided by a ring.

Above the ring the stipe is yellow, often the same lemon as the pores, and finely dotted or faintly netted at the very top where the tubes run down. Below the ring it is streaked, smeared and often coarsely net-marked in brown, reddish brown or rusty tones over a yellow ground, and it grows browner towards the base.

The ring itself starts as a whitish to pale yellow membranous veil connecting the cap margin to the stipe. It is often gelatinous or sticky on its underside, and after the cap expands it collapses into a soft, sometimes slimy band that can smear or vanish in old specimens. Look for the colour boundary even when the ring has gone: yellow above, brown-streaked below, with a sharp line between them.

The base may carry pale yellow to whitish mycelial threads binding needles and soil.

Flesh and Colour Change

Cut the fruitbody in half from cap to base. The flesh is pale to bright yellow, deeper near the tubes, and often flushed brownish or reddish in the stipe base. On exposure it usually changes slowly to pinkish, vinaceous or brownish, especially in the stipe; some collections barely react at all. Nothing turns rapidly blue.

The texture is soft and slightly spongy in the cap and firmer in the stipe, and old fruitbodies waterlog quickly, going flabby after rain.

Taking a Spore Print

Trim the stipe off flush with the tubes, set the cap pores-down on white paper, and cover it with a bowl for six to twelve hours in still air at room temperature. The gluten on top of the cap makes for a messy job, so put a piece of card under the whole arrangement.

The deposit is ochre-brown to olive-brown, warm rather than cold in tone. Spores under a microscope are smooth, elongate-ellipsoid, about 8 to 11 by 3 to 4 micrometres. A pale, pink or dark purple print would mean you had strayed out of the genus.

Substrate and Season

Ectomycorrhizal with larch and only larch, growing from soil, grass or needle litter and never from wood. It follows larch wherever the tree is planted, which is most of temperate Europe, North America and beyond, so it turns up in urban parks and gardens as readily as in forestry blocks. Fruiting runs from July to November, with heavy flushes after autumn rain, and it is one of the more dependable boletes to find year after year in the same spot.

Separating It From Look-alikes on Morphology Alone

Suillus tridentinus also grows with larch but has a duller orange to orange-brown cap that is finely fibrillose-scaly rather than smoothly glossy, and its pores are distinctly orange and elongated or radially arranged rather than small, round and lemon.

Suillus viscidus (the grey larch bolete) shares the host and the ring but is dull grey, greyish-buff or clay coloured overall, with wide greyish angular pores, and its flesh often flushes blue-green in the stipe base.

Suillus clintonianus is a larger, darker larch associate with a deep chestnut to mahogany cap and a more strongly developed ring, and is best separated by the depth of cap colour and stouter build.

Suillus luteus grows with two-needle pines, not larch. Its cap is dark chocolate to purple-brown, and its ring is a conspicuous, firm, membranous collar with a violet-brown stained underside, quite unlike the soft yellowish band here.

Suillus granulatus and Suillus collinitus are pine associates with no ring at all and milky droplets on young pore surfaces.

Suillus cavipes grows with larch too but has a dry, brown, hairy-fibrillose cap and, decisively, a hollow stipe at maturity.

Suillus lakei has a dry brick-red scaly cap and wide radial pores, and it partners Douglas fir rather than larch.

Field Summary

Larch overhead, glossy sticky golden to chestnut smooth cap with a peelable skin, small lemon-yellow pores bruising slow rusty brown, a soft whitish ring dividing a yellow upper stipe from a brown-streaked lower one, yellow flesh with a slow pinkish-brown change, and an ochre-brown spore print.