Scarletina Bolete Identification Guide

First impression

The usual encounter is under beech, oak or birch on acid ground, or along a mossy ride in a spruce plantation, in late summer. What catches the eye is a solid, dark-capped bolete, the cap a deep chestnut to olive-brown with a matt velvety bloom that reads almost black in shade. Then you tip it and the underside is startling: a dense sheet of deep orange-red to blood-red pores. The stipe is thick, yellow at a distance but flushed orange-red over its length by countless minute dots.

Fruitbodies are frequently large, 10 to 20 cm across in a good season, and they are often solitary or in small scattered groups on sloping banks and track edges rather than in deep leaf litter.

Reading the cap

The cap is 5 to 20 cm across, hemispherical with an inrolled margin when young and expanding to convex or broadly cushion-shaped. The surface is dry and finely velvety, like short suede, becoming smoother and slightly greasy in wet weather or in old age. Colours range through dark bay-brown, chestnut, olive-brown and nearly blackish-brown, sometimes with an ochre or olive flush at the margin and occasional reddish tones in exposed caps.

Press the cap firmly with a thumb. It bruises blue-black promptly, and old caps often carry a history of dark thumbprints and slug scrapes. Note that the cap has no whitish or pale grey phase, which immediately separates it from the pale-capped members of the group.

The pore surface

The pores are the second big character. They are minute, about two or three to the millimetre, circular, and deep orange-red to blood-red across most of the surface, usually with a narrow yellow zone at the extreme cap margin in young fruitbodies. Very old or deeply shaded specimens can yellow overall, so judge a fresh, well-coloured fruitbody where possible.

Press the pore surface with a finger. The change is immediate and dramatic: red to a very dark blue-black in a second or two, with a sharply defined fingerprint. The tube layer behind is yellow to olive-yellow, 1 to 2 cm deep, adnexed to depressed around the stipe apex, and it blues just as quickly on a vertical cut.

The stipe: dots, not a net

The stipe is stout, 5 to 15 cm tall and 2 to 5 cm thick, club-shaped when young and becoming more cylindrical. From a couple of metres away it looks orange-red, but the correct reading needs a lens. The ground colour is bright yellow, and over it lies a dense covering of fine, separate red to orange-red dots, or punctae, which crowd together in the lower half and can merge into vague vertical streaks near the base.

What you must confirm is a negative: there is no raised mesh. Run a fingernail up the stipe and look at it in side light. Dots are isolated granules on an otherwise even surface; a network is a continuous system of raised ridges with sunken cells between them. This dots-versus-net test is the pivot of the whole red-pored bolete group and it is worth thirty seconds and a clean patch of stipe. The very base is often browner or reddish-brown and bound with yellow mycelial threads.

Flesh and colour change

Cut the fruitbody vertically from cap centre to base in one clean stroke and watch the cut face. The flesh is bright lemon-yellow and turns intensely dark blue almost instantaneously throughout the cap and stipe, so quickly that photographing the yellow phase takes practice. Over twenty to thirty minutes the blue dulls to a greyish or blackish blue. The very base of the stipe may show wine-red or reddish-brown tints in the flesh.

While the cut is fresh, check for a thin red line along the boundary between the tube layer and the cap flesh. In this species there is none; that line belongs to the Lurid Bolete. The smell is mild and unremarkable, and there is no latex or gelatinous layer.

Spore print

Sever the cap, place it pore-side down on white paper under a cover, and leave it for several hours or overnight. Mature caps deposit heavily. The print is olive-brown, the standard colour for the group, and it rules out unrelated pale-printing or dark-printing genera. Under the microscope the spores are smooth, subfusiform and roughly 12 to 17 by 5 to 6.5 micrometres.

Habitat and season

The species is ectomycorrhizal, so the tree list is part of the identification. It partners with beech, oak and birch on acid, sandy or peaty soils, and with spruce and pine in upland plantations, and it can be locally abundant on mossy banks, heathy woodland edges, parkland and the sides of forest tracks. The season runs from early summer to late autumn, peaking after warm rain in late summer. It favours well-drained, acidic ground and is scarce on chalk and limestone, which is a useful geographic filter when several red-pored boletes are possible.

Separating it from look-alikes on morphology alone

• Lurid Bolete, Suillellus luridus: cap paler, tan to olive-buff rather than dark chestnut; the stipe carries a coarse raised red network, not dots; and a vertical cut shows a thin red line immediately above the tube layer. Commoner on calcareous ground.
• Scarlet-stemmed Bolete, Caloboletus calopus: a pale grey-buff cap and lemon-yellow pores, never red, with a red lower stipe carrying a distinct raised network.
• Devil's Bolete, Rubroboletus satanas: whitish to pale grey cap, blood-red pores, a squat bulbous stipe with a fine red net over yellow, and a much weaker and slower blue reaction; a calcareous-soil species.
• Rubroboletus legaliae and relatives: cap flushed pink or apricot, red pores, and a fine red network on the stipe.
• Suillellus queletii: cap brick to apricot-brown, stipe finely dotted but with beetroot-red flesh in the extreme base, and an association with willow and oak on heavier or sandy calcareous soils.
• Imperator torosus and relatives: massive, with olive to ochre caps and very dense flesh, and the blueing pattern differs.
• Chalciporus piperatus: small and slender, with a tawny cap and rusty-cinnamon angular pores that do not blue, and yellow flesh in the stipe base.

The four-step check

Dark velvety brown cap; red pores that blue instantly; a yellow stipe covered in separate red dots with no network; yellow flesh turning immediately deep blue with no red line above the tubes. If all four hold and the print is olive-brown, the identification is secure. If a raised mesh appears under the lens, or the cap is pale, stop and run through the alternatives above.