Bronze Bolete

Description

The Bronze Bolete is a large, stocky bolete with a dark, velvety cap, usually 15–20 cm across, in colours from dark brown to purplish brown, often with coppery patches. The underside consists of small pores, white at first, which turn yellow and then green with age. The stem is thick, barrel-shaped, brownish, covered with a dark net-like reticulation. The white flesh smells pleasantly nutty and does not change colour when cut.

It grows in warm broadleaved forests and parks, under oaks, beeches and sweet chestnuts, from May to September. In Poland it is very rare and appears on the Red List as an endangered species.

It is most easily confused with other boletes from the porcini group. The summer bolete has a paler cap and a more distinct, light reticulation on the stem, while the porcino is paler and has a stem without a dark reticulation. If you are not sure of the species, do not pick it and do not eat it.

Identification features

Cap

Diameter usually 15–20 cm, up to 30 cm (specimens up to 40 cm have been recorded); thick, fleshy, sometimes wrinkled. Hemispherical when young, then convex, finally flat. Surface dry, at first slightly velvety, later smooth and bare, sometimes cracked. Colour dark brown, chestnut brown, greyish brown or purplish brown, often with coppery, golden or olive patches.

Hymenophore (underside of the cap)

Tubes up to 3 cm long, separating easily from the cap flesh; white or cream in young fruiting bodies, yellowish olive to olive green in older ones. Pores small, round, whitish when young, becoming yellowish to greenish yellow with age; when damaged they may turn wine-coloured (descriptions differ on the colour change).

Stem

Height 5–15 cm, thickness 2–5 cm, usually shorter than the cap diameter. Barrel-shaped and swollen in young fruiting bodies, later club-shaped or cylindrical, narrowed at the base. Colour from whitish through pale brown and chestnut to reddish brown, covered with a brownish or concolorous net-like reticulation. No ring.

Flesh

White, brownish only under the cap skin; very firm at first, softer later. Does not change colour on exposure to air. Smell mushroomy, distinct, reminiscent of hazelnuts; taste mild, slightly sweetish.

Spore print and spores

Spore print olive to olive brown. Spores smooth, spindle-shaped, usually 13–16 × 4–5 µm (descriptions give wider ranges, up to 10.5–19 × 4–7 µm).

Habitat and distribution

Ecology. Mycorrhizal fungus (ectomycorrhiza) with broadleaved trees and shrubs, especially oaks (including cork oak), beeches and sweet chestnut, as well as strawberry tree, heath and rockroses; prefers acidic soils. A heat-loving species; fruiting bodies most often appear in hot periods of summer and autumn. Also grows by roadsides and in parks.

Distribution. Europe (mainly the Mediterranean basin and south-eastern regions; rare elsewhere), North Africa; according to some descriptions also North America, Korea and Japan, although more recent molecular studies indicate that the Asian and some North American boletes are different species. Very rare in Poland, on the Red List of Plants and Fungi of Poland with category E (endangered, critically threatened); also placed on red lists in, among others, the Czech Republic, Germany, Denmark, Lithuania, Norway and the Netherlands. Not legally protected in Poland (Dz.U. 2014 poz. 1408).

Fruiting. From May to September (in Mediterranean regions also in autumn, and locally even in winter).

What can it be confused with?

• Boletus reticulatus (summer bolete) — Paler, often cracked cap without chestnut-brown and blackish shades; paler stem with a more distinct, whitish reticulation, often reaching the base.
• Boletus edulis (porcino) — Paler cap, sticky in wet weather; paler stem with a sharp, white reticulation. Grows later in the season, at lower temperatures, mainly under spruces. Microscopically it has gelatinised ends of the cap skin hyphae.
• Boletus pinophilus (pine bolete) — Grows under conifers, mainly under Scots pine; cap reddish brown. Microscopically it has more swollen, club-shaped to spindle-shaped ends of the cap skin hyphae.
• Butyriboletus regius (royal bolete) — Caution: similar protected species (strict protection in Poland), not included in the Atlas. Cap pink to rose-red, tubes and pores bright yellow, stem yellow with a fine yellow net, flesh yellow. Do not pick.

Never rely on a single feature. If you are not sure — do not pick it; show the mushroom to a qualified mushroom expert.

Interesting facts

• Described by Pierre Bulliard in 1789; Bulliard called it le bolet bronzé in French and noted that in other countries it was called the "black bolete".
• In various languages it has poetic names: in Greek vasiliko ("royal") and kalogeraki ("little monk"), in Italian porcino nero, in Basque ontto beltza ("black mushroom").
• Around Borgo Val di Taro in Italy, the Bronze Bolete, porcino, summer bolete and pine bolete are covered by the common designation of origin Fungo di Borgotaro; they have been collected and exported there for centuries.
• On the island of La Gomera (Canary Islands) it can be found even in February; in some supermarkets in Germany it is sold at a very high price.