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Cap surface

Cracked

Cracked — mushrooms with the trait «Cracked»

A cracked (areolate, cracked) cap surface is a remarkable phenomenon in mycology, in which the mushroom's outer skin (cuticle) tears, forming a network of cracks. The cap starts to look like a mosaic, old asphalt, the bed of a dried-up lake or a giraffe's hide. The inner flesh, often in a contrasting color, always shows through these deep cracks.

12 species in the database.

Why caps crack

David Arora explains that cracking has mechanical causes. In some mushroom species the cuticle is very dry, rigid and inelastic. When the flesh of the cap, fed by moisture from the soil or driven by high temperatures, starts to swell sharply and quickly (expand), the outer skin "can't keep up" with this growth. It simply bursts under the tension. This most often happens in dry, windy or hot weather.

Classic cracked mushrooms

For some species this trait is so consistent that it has become an official feature of the species:

1. Red cracking bolete (Xerocomellus chrysenteron): The benchmark for this texture. Its olive-brown velvety cap tears into deep cracks. The key feature is that the flesh showing in these cracks is bright red or pinkish purple.

2. Greencracked brittlegill (Russula virescens): One of the best and tastiest edible mushrooms. Its pale green or copper-green cap breaks up into characteristic angular "scale islands" (areolae), with white flesh visible between them. Its surface looks like crackled ceramics.

3. Porcini (Boletus edulis): During long, harsh summer droughts (especially at forest edges), porcini's perfectly smooth cap can crack deeply, forming square "tiles."

Danger in the cracks

Cracking makes a mushroom extremely vulnerable. Bacteria, mold spores and insects (fungus gnats that lay their eggs) get into the cap through the cracks in no time. That's exactly why badly cracked Xerocomus boletes very quickly become wormy or get covered in a layer of white parasitic mold (mushrooms infected with it must not be eaten).

Questions and answers

If a porcini has cracked, can you still eat it?
Yes, cracking is just a reaction to dry weather; it doesn't produce any poisonous substances in the mushroom. Still, be sure to cut such a mushroom open and check that it hasn't been spoiled inside by mold or insect larvae, which could easily get in through the cracks.
How is a scaly surface (like the parasol's) different from a cracked one (like a Xerocomus bolete's)?
They form in similar ways, but the result is different. On the parasol mushroom the skin tears and its edges curl upward or flake off easily (like real fish scales). On a cracked Xerocomus bolete or the greencracked brittlegill, the skin pulls apart like cracked earth, but the islands of skin stay pressed tight against the flesh (they don't curl up).

Sources

  1. 1.Зерова М.Я. та ін. Визначник грибів України. 1979
  2. 2.Roger Phillips. Mushrooms (Roger Phillips)
  3. 3.David Arora. Mushrooms Demystified
  4. 4.Index Fungorum