How to identify a slippery jack: the key features

The slippery jack is one of those mushrooms that practically beg to go in your basket: easy to spot, growing in little families, and with a few very clear features. Still, beginners sometimes hesitate over whether it's really a slippery jack. Let's settle once and for all what to look at.

The good news: to confidently recognize a slippery jack (Suillus luteus and close relatives), you only need to check a few simple traits. Look the mushroom over from top to bottom, and your doubts will vanish.

Feature one: a slimy cap

The first thing that catches your eye is the glossy, slimy cap. That's exactly how the slippery jack got its name: the film on the cap looks as if the mushroom had been greased with oil.

In wet weather the slime is especially noticeable, and the cap positively gleams. In dry weather it dries out, dulls and turns slightly tacky to the touch. The color depends on the species: from chocolate brown in the slippery jack to yellow in the larch bolete.

If the cap is dry and matte, it's either an old mushroom or one of its drier relatives, such as the bovine bolete or the velvet bolete. In that case, check the other features more carefully.

Feature two: a spongy underside

Now turn the mushroom over. Under the cap of a slippery jack there's a spongy layer of tubes that looks like a fine, soft sponge, not gills.

This is the most important safety sign. All slippery jacks have tubes, so if you see gills under the cap, it's definitely not a slippery jack. The color of the sponge changes with age:

• in a young mushroom it's pale yellow, sometimes covered by a white veil;
• in a mature one it's bright yellow;
• in an old one it's dark olive and soft.

Old mushrooms with a darkened sponge are best left in the forest.

Feature three: a ring or granules on the stem

Look at the stem. The slippery jack and larch bolete have a ring on it, what's left of the veil that covered the young sponge.

The weeping bolete has no ring, but its stem shows tiny milky-colored granules, like little droplets. Both the ring and the granules are reliable clues that you're looking at a slippery jack.

Here it all is in one short rule:

1. a slimy, glossy cap;
2. a spongy, not gilled, underside;
3. a ring or granules on the stem.

All three match? There's practically no doubt.

Where this check matters most

Slippery jacks grow under pines and larches, that is, in coniferous and mixed forests. The tree is a clue too: a true slippery jack won't grow in the middle of a deciduous grove with no conifers nearby.

The best time to go is a day or two after a warm rain, when slippery jacks come up en masse. These windows are easy to track with our mushroom radar: it shows when moisture and warmth line up well for mushrooms to appear.

Caution never hurts

The slippery jack is one of the safest mushrooms, because it has practically no dangerous lookalikes. But the habit of checking features is useful for any mushroom. The main thing to remember: a spongy underside means a slippery jack; gills under the cap are a reason to stop. And, as always: if you're not sure, don't pick it.

Sources

• «Key to the Fungi of Ukraine» (Kyiv, Naukova Dumka publishers).
• Suillus luteus on GBIF, a global biodiversity database.
• Suillus on MycoBank, an international fungal nomenclature database.
• Suillus luteus on Wikipedia.