King Bolete Identification Guide

The First Impression

A good King Bolete announces itself by proportion before colour. What you see is a heavy, rounded, brown cap sitting on a barrel of a stipe that is often as wide as it is tall, the whole thing looking as though it has been pushed up through the litter rather than grown out of it. Young buttons are almost spherical, the cap gripping the stem like a cork in a bottle. The species is known regionally as the cep or penny bun, and the second of those names is a fair description of the mature cap.

You will usually be standing in mature forest with a decent litter layer, under spruce, pine, beech or oak, often on the mossy edge of a track or in the half-shade at the border of a clearing. Fruitbodies come singly, in loose arcs, or occasionally in rings, and they push up in flushes a few days after soaking rain.

Reading the Cap

Caps commonly reach 8 to 20 cm and exceptionally far more. The shape starts hemispherical, becomes a broad convex dome and eventually flattens somewhat, but the margin stays thick and rounded rather than thinning to a blade.

Colour ranges from pale tan and biscuit through chestnut to a deep chocolate brown, usually darkest at the centre and paler towards the rim. On young fruitbodies look closely at the extreme margin: there is very often a narrow whitish or cream band, a fine bloom that survives until the cap expands. It is a small character but a genuinely useful one.

The surface is smooth and dry in fair weather with a faint sheen; after rain it becomes slightly greasy or tacky to the touch, though never truly slimy. Wrinkling and shallow pitting are common on large caps, but the cap skin does not crack into a tiled mosaic the way some relatives do.

The Pore Surface Through Its Ages

The underside changes with age and you should describe it by stage rather than by a single colour. In buttons the pores are white and so tightly packed that the surface looks like a felted pad, almost solid. As the fruitbody matures they open, turn cream, then a clear yellow, and finally a dull olive or olive-brown in old caps. The tube layer becomes thick, spongy and easily separated from the cap flesh with a thumb.

Pores are small and round, and the layer is depressed around the top of the stipe. Now bruise them firmly. In this species nothing much happens: the surface may dull slightly or take a faint brownish smudge, but it does not go blue. That absence of blueing, checked on both pores and cut flesh, is one of the two or three characters that carry the identification.

The Stipe and Its Net

The stipe is stout, 8 to 20 cm tall and often 3 to 7 cm thick, swollen or club-shaped in youth and becoming more cylindrical as the cap expands. It is white, cream or pale buff, sometimes flushed the same brown as the cap over the lower half in older specimens.

Hold it in good light and look at the upper third with a lens. You should see a fine, raised, white reticulation, a delicate net of ridges that is most obvious just under the tubes and fades out downwards. The net is pale on a pale ground, which makes it easy to miss; tilt the stipe until the ridges catch the light. The mesh is fine and even, not coarse, and it is never dark brown or black.

At the base, white mycelial cords bind soil and needles into a pad. Lift the whole fruitbody rather than cutting at ground level so this is preserved.

Flesh and Colour Change

Split the fruitbody from cap to base. The flesh is white, firm, and thick, staying white immediately under the cap skin except for a thin brownish or vinaceous line directly beneath the cuticle in some collections. Watch the face for several minutes: it remains white. There is no blue, no pink, no grey and no blackening. Older or waterlogged specimens go softer and slightly buff, but the colour does not shift dramatically.

Check too for insect tunnels while the fruitbody is open, and note the texture of the stipe core, which should be solid and fibrous rather than hollow or chambered.

Taking a Spore Print

Slice a mature cap free, lay it pore-side down on white paper, and cover it with a bowl for six to twelve hours in a still, room-temperature spot. Thick tube layers hold moisture, so overnight is realistic. The deposit is olive-brown to a dull yellow-brown, thick and even. Under the microscope the spores are smooth, narrowly spindle-shaped, roughly 14 to 18 by 4.5 to 6 micrometres.

A pink or flesh-coloured print takes you straight out of Boletus and into Tylopilus, which is exactly the comparison you most need.

Substrate and Season

Boletus edulis is ectomycorrhizal, forming partnerships with the roots of living trees. Spruce and pine are its commonest hosts across northern Europe and North America, with beech and oak important further south. It fruits on soil, never on wood, from midsummer through late autumn, with the biggest flushes after warm rain in late summer and early autumn. It tolerates a wide range of soils and altitudes, from coastal pine dunes to montane spruce.

Separating It From Look-alikes on Morphology Alone

Tylopilus felleus is the classic confusion. Its pores start white but soon turn a distinct pink or flesh colour, its spore print is pink-brown, and its stipe carries a coarse, strongly raised, dark brown network that stands out clearly against a paler ground rather than the fine white mesh of the King Bolete.

Boletus reticulatus (also called B. aestivalis) is a genuine sibling. Its stipe is netted over almost its whole length, the cap is drier, duller and often finely cracked in a mosaic, and it fruits earlier in summer, mostly with oak and beech.

Boletus pinophilus has a dark red-brown to mahogany cap, often with a purplish cast, a stipe flushed the same brown with a reddish net, and a preference for pine.

Imleria badia has a bay to chestnut cap that is tacky when wet and yellowish pores that flush blue-green promptly when pressed, with only a smooth stipe and no net at all.

Neoboletus and Suillellus species have orange to red pore mouths and flesh that turns blue instantly.

Caloboletus calopus has a pale grey cap, yellow pores, a stipe with a red zone and a vivid red net, and flesh that blues strongly.

Leccinum species look superficially similar in outline but have stipes covered in rough dark scabers rather than a raised net, and flesh that usually darkens grey or black on cutting.

The Confirmation Set

Brown bun-shaped cap with a pale rim, pores white then yellow then olive and never blueing, swollen pale stipe with a fine white net on the upper part, unchanging white flesh, growth on soil with spruce, pine, beech or oak, and an olive-brown spore print.