Caloboletus calopus

Caloboletus calopus: A Fungus with a Bitter Secret

The Enigmatic Caloboletus calopus

Imagine stumbling upon a mushroom that looks like it could be a delicacy, only to find out its taste is as bitter as the medicine you take when you’re sick. That’s what Caloboletus calopus is all about. This fascinating fungus has a history dating back to 1801, when Christiaan Persoon first described it under the name Boletus calopus. But in recent years, its classification has undergone some interesting changes.

A New Home for an Old Fungus

Caloboletus calopus was transferred to a new genus called Caloboletus by Italian mycologist Alfredo Vizzini in 2014. This move was based on genetic analysis, which showed that it was only distantly related to the type species of Boletus. The name change reflects the unique characteristics of this fungus and its place within the fungal kingdom.

Physical Description: A Mushroom with a Story

The cap of Caloboletus calopus can grow up to 15 cm across, ranging in color from beige to olive. It starts off globular but eventually becomes hemispherical and convex as it matures. The surface is smooth or has minute hairs that sometimes develop into cracks with age. Beneath the cap, you’ll find yellow pores that turn blue when injured, and a stipe that can be up to 15 cm long and 5 cm wide. The stipe is typically yellow above but turns pink-red below, often with a straw-colored network near the top or over the upper half.

Spore Print and Other Characteristics

The spore print of Caloboletus calopus is olive to olive-brown, and its spores are smooth and elliptical. The basidia are club-shaped, four-spored, while the cystidia are club-shaped to spindle-shaped and hyaline. There are also varieties within this species: Caloboletus calopus var. frustosus has an areolate cap in maturity, var. ereticulatus has fine reddish granules on the upper stipe, and var. ruforubraporus has pinkish-red pores.

Similar Species: A Mushroom with a Lookalike

While Caloboletus calopus stands out due to its unique coloration, it can be mistaken for other species like Suillellus luridus or Rubroboletus satanas. Its large pale specimens might resemble the former, while the cap of the latter is similar but with red pores. In poor condition, it could also be confused with Xerocomellus chrysenteron. It closely resembles C. radicans, lacking redness on the stipe. Like Caloboletus calopus, Boletus coniferarum has a bitter taste and similar characteristics but lacks reticulation on its reddish stipe.

Ecology: A Fungus in Its Natural Habitat

Caloboletus calopus is an ectomycorrhizal species that grows in coniferous and deciduous woodland at higher altitudes. It can be found singly or in large groups on chalky ground from July to December in Northern Europe, the Pacific Northwest of North America, and Michigan. Its range extends south to Mexico, with variety frustosus known from California and the Rocky Mountains of Idaho.

Eating Caloboletus calopus: A Bitter Experience

Despite its unique appearance, Caloboletus calopus is not typically considered edible due to its intensely bitter taste. However, there are reports of it being consumed in eastern Europe, particularly in far eastern Russia and Ukraine. The bitterness comes from compounds like calopin and O-acetylcyclocalopin A. Pulvinic acid derivatives inhibit cytochrome P450 enzymes, while other compounds include calopin B, cyclopinol, boletunones A and B, with significant free-radical scavenging activity.

Conclusion: The Tale of a Bitter Mushroom

Caloboletus calopus is more than just a mushroom; it’s a story of transformation, from its initial description as Boletus calopus to its current classification in the genus Caloboletus. Its bitter taste and unique characteristics make it a fascinating subject for mycologists and nature enthusiasts alike. Whether you’re looking for a new addition to your collection or just curious about the diverse world of fungi, this enigmatic species is definitely worth exploring.