Bronze Bolete
Boletus aereus
Also called dark cep, queen bolete, black-headed bolete
The darkest member of the porcini group, with a sooty bronze to almost black velvety cap over a brown stipe finely netted in pale lines. Flesh white and unchanging.
Overview
Boletus aereus is the southern, dark-capped member of the Boletus edulis complex and one of the most striking large boletes in Europe. The specific epithet refers to bronze, and a mature cap really does look like tarnished metal: dark umber to sooty black, dry, matte and faintly velvety, often blotched with paler bronze or coppery patches.
It belongs firmly in Boletus in the strict sense, sharing the group's white unchanging flesh, pale pores that yellow with age and reticulate stipe. Its distinguishing features are the depth of the cap colour, the browner stipe with a fine pale net, and a marked preference for warm Mediterranean and sub-Mediterranean broadleaf woodland.
Where it occurs it is often the most conspicuous large fungus of late summer oak woods, and its dark cap against leaf litter makes it surprisingly easy to overlook until the pale stipe catches the eye.
How to identify it
Cap
The cap is 7-20 cm across and sometimes larger, hemispherical with a strongly inrolled margin when young, expanding to a broad cushion. Colour is dark bronze, umber, sooty brown or nearly black, often mottled with lighter coppery or ochre patches and paler towards the margin in age. The surface is dry, matte and finely velvety, and may crack shallowly in drought.
Pores
The pore surface is white and stuffed when young, ageing through cream to yellow and finally to dull olive-yellow. Pores are small, round and depressed around the stipe apex; the tube layer separates cleanly. There is no blueing when the pores are pressed.
Stipe
The stipe is stout, 6-15 cm tall and 3-7 cm thick, bulbous when young and becoming club-shaped or nearly cylindrical. Its ground colour is a warm ochre-brown to hazel, distinctly darker than the whitish stipe of B. edulis, and it is covered over the upper half or more by a fine raised network that is paler than the ground and can look almost white against the brown.
Flesh & spore print
The flesh is firm, thick and white, staying white when cut throughout cap and stipe. The spore print is olive-brown.
Where and when it grows
The Bronze Bolete is a fungus of warm, sunny broadleaf woodland. Its principal partners are evergreen and deciduous oaks, sweet chestnut, beech and holm oak, and it is most abundant in Mediterranean maquis-edge woodland, dehesa, chestnut coppice and open oak forest on well-drained soils. It seldom ventures into dense shade or cold soils.
Fruiting runs from midsummer into autumn, generally following late-summer thunderstorms. The species is common in southern and central Europe, particularly Iberia, France, Italy and the Balkans, reaching its northern limit in southern Britain and the warmer parts of central Europe, and extends into North Africa and western Asia.
Ecological role
Boletus aereus is ectomycorrhizal, forming sheathed root tips on oaks, chestnut and beech. The fungal mantle and the internal network between root cells give the tree access to a far greater volume of soil water and mineral nutrients, which matters particularly in the seasonally dry Mediterranean climates where this species is most at home; in return the fungus receives carbohydrates it cannot manufacture itself.
Fruit bodies typically emerge a week or two after significant rain breaks a dry spell, and their thick flesh allows them to persist for several days in warm conditions. As with other large boletes, insect larvae, small mammals and gastropods burrow through the flesh and carry spores beyond the reach of simple wind release from the tube layer.
Similar species
Boletus edulis is much paler, tan to chestnut with a pale marginal rim, and has a whitish stipe with a white net. Boletus reticulatus is mid-brown with a dry cracking cap and a pale net running the full length of the stipe. Boletus pinophilus is deep reddish mahogany rather than sooty bronze and grows with conifers on sandy acid soils.
Tylopilus felleus can approach it in cap tone but shows pinkish pores in age and a coarse dark brown net on a pale stipe. Dark-capped Xerocomellus species are separated by their much smaller size, cracking caps with reddish flesh in the fissures, angular yellow pores and flesh that often flushes blue.