Mushrooms often turn blue when cut, bruised, or handled. This striking color transformation is a natural chemical reaction occurring within the mushroom’s tissues. It frequently prompts questions about the mushroom’s identity and its potential edibility. Understanding this phenomenon involves exploring the biochemical processes that give rise to this vivid change.
The Science Behind the Blue Stain
The blue discoloration in certain mushrooms is a result of an oxidation reaction when compounds within the mushroom’s flesh are exposed to air. This process involves specific chemical molecules and enzymes. In psychoactive species, such as those from the genus Psilocybe, the blue color stems from the oxidation of psilocin, a compound derived from psilocybin. Enzymes dephosphorylate psilocybin to psilocin, which is then oxidized, leading to the formation of blue quinoid psilocyl oligomers.
For many bolete mushrooms, a different set of compounds is responsible for the blueing reaction. The color change often involves the oxidation of pulvinic acid derivatives, such as variegatic acid or xerocomic acid. When these compounds come into contact with oxygen, they are enzymatically converted into blue-colored quinone methide anions, producing the characteristic blue pigment visible in the injured parts of the mushroom.
Mushrooms That Turn Blue
Many mushroom species across various genera exhibit the blue-staining reaction. Among the most well-known are species within the Psilocybe genus, including Psilocybe cubensis and Psilocybe cyanescens, where blueing is a diagnostic feature. Numerous bolete species also display this phenomenon, such as Boletus erythropus, Boletus sensibilis, and Boletus campestris. These boletes can show a range of blueing intensity and speed.
Another notable example is Gyroporus cyanescens, often called the bluing bolete, recognized for its intense blueing when cut. The genus Porphyrellus, particularly Porphyrellus porphyrosporus, also includes species known for their blue-staining flesh and pores. The exact shade and rapidity of the blue stain can vary significantly.
Does a Blue Stain Indicate Toxicity?
A common misconception is that all blue-staining mushrooms are either toxic or psychoactive. However, a blue stain does not universally indicate toxicity or edibility. While some blue-staining boletes are indeed poisonous, such as Boletus satanas and certain Rubroboletus species, others are considered edible. For instance, Gyroporus cyanescens, despite its strong blueing reaction, is a widely regarded edible mushroom after proper cooking.
The blueing in Psilocybe species is a key indicator of the presence of psychoactive compounds like psilocybin and psilocin. These mushrooms induce significant psychological effects and are often illegal. Relying solely on a blue stain for identification can be dangerous, as many deadly mushrooms do not bruise blue, and some edible ones do. Accurate mushroom identification requires careful consideration of multiple features, including spore print, habitat, and overall morphology, rather than just color change.
Other Color Changes in Mushrooms
Beyond blue, mushrooms can exhibit a variety of other color changes when their tissues are damaged, all stemming from similar oxidative chemical reactions. Some species bruise red, such as certain Russula and Lactarius mushrooms, or Agaricus benesii, which shows a pinkish-red bruise. Other mushrooms may turn yellow upon bruising, exemplified by some Agaricus species, or exude white latex that dries to a deeper yellow, as seen in Lactarius chrysorrheus.
Certain mushrooms can also bruise black or brown, a common reaction in many polypores and puffballs. These diverse color shifts highlight the wide array of chemical compounds present in different fungal species. Just as with blueing, these color changes are a result of internal compounds reacting with oxygen, forming new pigments.