Blue-bruising boletes: which ones turn deep blue when cut

Ever cut a bolete open and watched the flesh flood with deep blue in a few seconds? In many regions people instantly call a mushroom like that a “syniak”. The catch is that this folk name hides not one species but at least three, and they're easy to mix up.

Let's sort out what the word “syniak” really means, which three mushrooms most often go by it and how they differ. Most importantly, we'll find out whether they're all edible and which features keep you from confusing a syniak with a genuinely dangerous bolete.

What a “syniak” is and where the name comes from

“Syniak” (literally “bruise”) isn't a scientific name but a folk one, given to mushrooms for one striking trait: they turn strongly and quickly blue when cut or touched. The color can range from light blue to dark blue, almost ink-like.

The bluing itself is completely harmless. It's ordinary oxidation of substances in the flesh when exposed to air, the same chemistry that makes a cut apple go brown. We covered the mechanism in more detail in a separate piece on why Xerocomus boletes turn blue when cut.

The problem lies elsewhere. Because the name “syniak” is tied only to the color of the cut, it easily gets attached to different species. So it's worth knowing the three main “contenders” for the name and being able to tell them apart.

Cornflower bolete, the truest syniak

If any mushroom deserves the name “syniak” most, it's the Cornflower bolete. It bruises instantly, dramatically and more intensely than any of the others: just press the cap or stem lightly, and within seconds the pale flesh turns a rich blue.

These features will help you recognize it:

• Cap. Dry, felty-granular, in straw-yellow or pale brown shades.
• Pores. Pale, whitish or pale yellow, with no hint of red.
• Stem. This is its calling card. Inside it's hollow and very brittle, snapping easily like a cookie.
• Cut flesh. White, but within a few seconds it turns intensely blue.

The Cornflower bolete is an edible and tasty mushroom. It grows on sandy soils in mixed and coniferous forests, often under birches and oaks. It's not very common, so finding one counts as a stroke of luck.

Inkstain bolete, the one that bruises in an instant

The second mushroom often called a syniak is the Inkstain bolete. Of all the Xerocomus boletes, it turns blue perhaps the fastest and most intensely, which is how it earned this folk name.

It's easy to tell it apart from the Cornflower bolete by a few details:

• Pores. Yellow or greenish yellow, unlike the whitish pores of the Cornflower bolete. They also turn blue instantly when pressed.
• Cap. Brown, olive-brown, often finely cracked, with a thin bloom as if dusted with powder. Hence the species name (pulverulentus, “powdered”).
• Stem. Solid, yellowish with brownish tints, not hollow.
• Cut flesh. Yellow, darkening to deep blue almost before your eyes.

This is an edible mushroom too. Like other Xerocomus boletes, it loves deciduous and mixed forests. If you want to get to know the Xerocomus group as a whole, start with our overview of what Xerocomus boletes are, then move on to individual species.

Scarletina bolete, the syniak with red pores

The third contender for the name “syniak” looks more alarming, because it combines intense bluing with red pores. This is the Scarletina bolete. Mushrooms like this are exactly the ones that scare beginners the most.

Its features:

• Cap. Large, velvety, dark brown or chestnut.
• Pores. Bright red or orange-red, turning blue instantly when touched.
• Stem. Yellow, densely covered with tiny reddish dots or grains, with no distinct net. Hence its Ukrainian name, meaning “grainy-stemmed”.
• Cut flesh. Yellow, rapidly bluing to a dark shade.

Here's an important, honest safety note. The Scarletina bolete is considered conditionally edible: you must not eat it raw; it needs thorough boiling for at least 15 minutes, discarding the water. Only after that is the mushroom fit for the table. If you're not sure of your identification, it's better to leave a red-pored bolete like this in the forest.

How not to confuse a syniak with a dangerous bolete

The main thing to remember: bluing by itself poisons no one. Excellent edible mushrooms turn blue too, such as the Bay bolete or Xerocomus boletes. Danger is given away not by the blue color but by entirely different features.

Pay special attention to boletes with red pores, because some truly dangerous species are among them. The best known is the Devil's bolete, a poisonous bolete with a whitish-gray cap, red pores and a red net on the stem. It turns blue too, so relying on the color of the cut alone is deadly unreliable here.

Here's what to look at instead of the bluing itself:

• Net on the stem. A red net pattern on the stem is a reason to be wary. The edible Scarletina bolete has a grainy, dotted stem, not a netted one. A red net is found on both the conditionally edible Lurid bolete and the poisonous Devil's bolete.
• Taste. Bitter or burning flesh is a bad sign. A sharp peppery taste, for example, gives away inedible species.
• Smell. A pleasant mushroomy smell is good; an unpleasant, chemical or rotten one is bad. The Devil's bolete starts to smell unpleasant as it ages.
• Cap color. A whitish-gray, dirty-looking cap combined with red pores is a reason not to pick the mushroom at all.

If you'd like to compare an edible red-pored bolete with its poisonous lookalike side by side, check out our comparison of the Scarletina bolete and the Devil's bolete. And to figure out when to head into the forest for boletes at all, use the mushroom radar: it shows when moisture and warmth line up well for mushrooms to appear.

To sum it up simply: “syniak” isn't one mushroom but a folk nickname for several boletes that bruise strongly blue. The Cornflower bolete and the Inkstain bolete are edible and safe, the Scarletina bolete is edible only after boiling, while the similar red-pored Devil's bolete is poisonous. So identify a mushroom by the whole set of features, not by the color of the cut alone.

Sources

• “Key to the Fungi of Ukraine” (Kyiv, Naukova Dumka publishing house).
• Gyroporus cyanescens on GBIF, a global biodiversity database.
• Neoboletus on MycoBank, an international fungal nomenclature database.
• Gyroporus cyanescens on Wikipedia.