Imleria badia, commonly known as the bay bolete, is an edible, pored mushroom found in Eurasia and North America, where it grows in coniferous or mixed woods on the ground or on decaying tree stumps, sometimes in prolific numbers.

Both the common and scientific names refer to the bay- or chestnut-coloured cap, which is almost spherical in young specimens before broadening and flattening out to a diameter up to 15 cm (6 in).

Modern molecular phylogenetic studies show Xerocomus to be polyphyletic (not descended from the same common ancestor), and the bay bolete is not particularly closely related to species in that genus.

Often considered a poor relation of the cep (Boletus edulis), I. badia is nevertheless regarded as a choice edible mushroom by some authors, such as food expert Antonio Carluccio, and is sold in markets in Europe and central Mexico.

Several European studies have demonstrated that the mushroom can bioaccumulate some trace metals from the soil, such as mercury, cobalt, and nickel.

[nb 1] Fries later renamed it as a variety of Boletus castaneus in 1828,[3] before assigning it distinct species status in his 1832 work Elenchus Fungorum.

[4] The fungus has been transferred to several genera in its taxonomic history: Rostkovites by Petter Karsten in 1881;[5] Viscipellis and Ixocomus by Lucien Quélet in 1886 and 1888, respectively;[6][7] and Suillus by Otto Kuntze in 1898.

The stickiness of its wet cap distinguishes the species from others classified in Xerocomus, and hence it was left in Boletus until Alfredo Vizzini placed it in its own genus in 2014.

[13] The species Boletus limatulus, originally published by Charles Christopher Frost in 1874,[14] was later redescribed, "with a slight tinge of irritation at the time, energy and gasoline spent", as a variety of I. badia by Wally Snell in 1945 (as Xerocomus badius var.

[17] Imleria badia fruit bodies have a chestnut to dark brown cap, which is almost spherical in young specimens before broadening and flattening out to a diameter of up to 15 cm (6 in).

Application of iron(II) sulphate solution causes the flesh to stain a dull bluish-green, while the pores turn golden brown with a drop of dilute potassium hydroxide.

Another lookalike is Austroboletus gracilis, but this species does not have a blue bruising reaction, and its pore surface is initially white before turning pinkish.

[28] Compared to I. badia, B. subtomentosus fruit bodies have narrower stipes, paler brown, dry caps,[29] and wider pores that do not stain blue on bruising.

[20] In western North America, I. badia is replaced by the similar B. zelleri, which also grows both on the ground and on rotten wood.

[30] The European species Xerocomus bubalinus can be mistaken for I. badia, but it has a paler yellow-brown cap flushed with pinkish-red, and is not sticky when wet.

[22] The ectomycorrhizae formed between I. badia and spruce (Picea abies) have active hyphal sheaths and a higher potential to store nitrogen, phosphorus, potassium, magnesium, iron, and zinc than other mycorrhizal types, indicating the fungus is well adapted to acidic stands and its mycorrhizae are very efficient in uptake and storage of macronutrients.

[40] Fruit bodies appear singly or scattered on the ground, or on decaying tree stumps, and can be well hidden by pine needles and ferns.

[22] It can also occur in grassy or mossy areas at or near forest margins;[21] Italian restaurateur and cook Antonio Carluccio recalled picking them in the grounds of Blenheim Palace.

[37] Often considered a poor relation of the cep (Boletus edulis), the bay bolete is nevertheless highly regarded as a choice edible mushroom by some authors such as Carluccio.

[39] It may cause an allergic reaction in some people,[43] and the blue discolouration upon bruising can be offputting,[41] although the staining disappears from white flesh when it is cooked.

Mushrooms can also be frozen, dried,[41] or pickled in cider vinegar, wine, or extra virgin olive oil,[45] and later used in sauces or soups.

Unprocessed mushrooms contain tryptophan (0.68 mg per 100 g dry weight), tryptamine (0.47), serotonin (0.52), kynurenine sulphate (1.96), and kynurenic acid (1.57).

[53][54] Similar conclusions about safety were made in a Polish study of the mushroom's ability to accumulate organochlorine compounds.