Slippery Jack Identification Guide

The first impression

Slippery Jack is a pine mushroom, and you will nearly always meet it in a plantation, a shelterbelt, a sandy heath or a dune ridge where Scots pine or a similar two-needle pine grows. The scene is typically a thin carpet of needles, some moss, and a scattering of dark, glossy caps that catch the light in a way no dry-capped mushroom does. Even from standing height the cap looks wet, varnished, almost lacquered, and pine needles and litter stick to it in clumps. The mushrooms are often gregarious, in loose troops or arcs following the tree roots, and they can appear in large numbers after autumn rain. Pick one up and the fingers come away slick.

Reading the cap

The cap is five to twelve centimetres across, sometimes larger, starting hemispherical and becoming broadly convex to almost flat. Colour is a rich chestnut, dark red-brown, purple-brown or sepia, sometimes streaked or mottled, generally darker in youth and fading to a duller yellow-brown or ochre-brown with age and sun. The defining texture is the thick layer of gluten covering the surface: in wet weather it is genuinely slimy, in dry weather it becomes sticky, shining and finally almost polished. That skin peels away from the cap flesh very readily, which is a useful confirmation of the genus. The margin is even and, in young specimens, connected to the stipe by a membranous veil that gives the underside a closed, sealed look.

The pore surface

Underneath there is a sponge, not gills. The tube layer is thin to moderately thick and adnate to slightly decurrent on the stalk. The pores are small, round to slightly angular, and arranged in an even fine mesh. Their colour begins pale lemon yellow and becomes a deeper yellow, then dingy ochre-yellow to olive-tinged in old age. There is no red or orange pore mouth, and the pores do not turn blue when bruised; they may discolour slightly brownish where handled. In young specimens the whole pore layer is hidden by the white to greyish veil stretched from cap margin to stipe.

The stipe, the ring and the glandular dots

The stipe is four to ten centimetres tall and one to two and a half centimetres thick, more or less cylindrical, sometimes slightly swollen below, firm and solid. It carries two features that together clinch the identification.

First, the ring. As the cap expands, the veil tears and leaves a conspicuous, membranous, rather floppy ring in the upper third of the stalk. Look at its underside: in fresh specimens it is stained violet, lilac or purple-brown, a detail that separates this species from most of its relatives immediately. Above the ring the stalk is pale yellow, whitish or lemon; below it, it is whitish to pale brownish, often becoming dingier with age. The ring can collapse into a sheathing band around the stalk in old, weathered specimens, so look for a violet-edged zone even when the flap has gone.

Second, the glandular dots. Under a lens, the surface of the stipe above the ring is scattered with tiny raised dots or granules, pale at first and darkening to brown or blackish. These are clusters of specialised cells and they are the shared signature of the genus. On this species they are largely restricted to the zone above the ring.

There is no volva, no bag and no rooting taproot; the base is simply rounded or slightly tapered, usually with white mycelium binding pine needles.

Flesh, section and colour change

Cut the mushroom lengthways. The flesh is soft, whitish to pale yellow, more yellow immediately above the tubes, and it is essentially unchanging on exposure: no blueing, no reddening, at most a slow dulling to a dingier cream. The tubes separate cleanly from the cap flesh if you push a thumb between them, which is another Suillus and bolete family trait. The odour is mild and slightly fruity or simply fungal.

Spore print

Set a mature cap pore-side down on white paper, cover it, and leave it a few hours. Two practical notes: the glutinous cap will glue itself to the paper, so support the cap on matchsticks, and give it plenty of time, as boletes drop spores more slowly than many gilled mushrooms. The print is a warm ochre to cinnamon-brown or clay-brown, sometimes with a faint olive cast, and it is duller and browner than the olive-brown of many other boletes.

Substrate, season and partnership

Suillus luteus is an obligate mycorrhizal partner of two-needle pines, above all Scots pine, and also Corsican, Austrian and Monterey-type pines in plantations worldwide. It has travelled with planted pine across the southern hemisphere and is common in exotic pine forestry. Look on sandy, acidic, well-drained soils in young to middle-aged stands, along ride edges, on mossy banks and in dune plantations. Fruiting is mainly late summer to late autumn and continues until sharp frosts. If your candidate is growing under larch or under broadleaf trees, the identification needs to change.

Separating it from look-alikes on morphology alone

The genus is easy: slimy or gluey cap, small yellowish pores, dots or a ring on the stalk, conifer host. Within it, the ring is the primary divider.

Weeping Bolete, Suillus granulatus, is the nearest relative that lacks a ring entirely. Its cap is paler, ochre to tawny or cinnamon rather than dark chestnut, and its glandular dots cover the whole length of the stipe. Young specimens exude milky white droplets from the pores, which dry to brown dots.

Suillus collinitus also has no ring, has a streaky brown cap and, decisively, pink to rosy mycelium at the stipe base, best seen by teasing the litter apart.

Bovine Bolete, Suillus bovinus, has no ring, a pale pinkish-buff to clay cap, and large, wide, compound, angular pores that look like a coarse honeycomb, quite unlike the fine pore mesh here.

Larch Bolete, Suillus grevillei, does have a ring, but its cap is bright golden yellow to orange or chestnut-yellow, its flesh is lemon yellow, and it grows only with larch.

Velvet Bolete, Suillus variegatus, has a dry to slightly tacky, finely scaly ochre cap, no ring, and flesh that blues slightly.

Outside Suillus, any bolete with a raised network on the stalk, or with red or orange pores, or with flesh that turns blue at once, belongs to another genus. The complete package here is: dark glutinous chestnut cap, fine lemon pores, glandular dots above a floppy ring with a violet underside, unchanging pale flesh, ochre-brown print, and a two-needle pine overhead.