Boletus aereus

Boletus aereus, the dark cep or bronze bolete, is a highly prized and much sought-after edible mushroom in the family Boletaceae. The bolete is widely consumed in Spain (Basque Country and Navarre), France, Italy, Greece, and generally throughout the Mediterranean. Described in 1789 by French mycologist Pierre Bulliard, it is closely related to several other European boletes, including B. reticulatus, B. pinophilus, and the popular B. edulis. Some populations in North Africa have in the past been classified as a separate species, B. mamorensis, but have been shown to be phylogenetically conspecific to B. aereus and this taxon is now regarded as a synonym. The fungus predominantly grows in habitats with broad-leaved trees and shrubs, forming symbiotic ectomycorrhizal associations in which the underground roots of these plants are enveloped with sheaths of fungal tissue (hyphae). The cork oak (Quercus suber) is a key host. The fungus produces spore-bearing fruit bodies above ground in summer and autumn. The fruit body has a large dark brown cap, which can reach 30 cm (12 in) in diameter. Like other boletes, B. aereus has tubes extending downward from the underside of the cap, rather than gills; spores escape at maturity through the tube openings, or pores. The pore surface of the fruit body is whitish when young, but ages to a greenish-yellow. The squat brown stipe, or stem, is up to 15 cm (6 in) tall and 10 cm (4 in) thick and partially covered with a raised network pattern, or reticulation. French mycologist Pierre Bulliard described Boletus aereus in 1789. The species epithet is the Latin adjective aerěus, meaning 'made with bronze or copper'. His countryman Lucien Quélet transferred the species to the now-obsolete genus Dictyopus in 1886, which resulted in the synonym Dictyopus aereus, while René Maire reclassified it as a subspecies of B. edulis in 1937. In 1940, Manuel Cabral de Rezende-Pinto published the variety B. aereus var. squarrosus from collections made in Brazil, but this taxon is not considered to be taxonomically distinct. In works published before 1987, the binomial name was written fully as Boletus aereus Fr., as the description by Bulliard had been sanctioned (i.e., treated as if conserved against earlier homonyms and competing synonyms) in 1821 by the 'father of mycology', Swedish naturalist Elias Magnus Fries. The starting date for all the mycota had been set by general agreement as 1 January 1821, the date of Fries' work. The 1987 edition of the International Code of Botanical Nomenclature revised the rules on the starting date and primary work for names of fungi; names can now be considered valid as far back as 1 May 1753, hence predating publication of Bulliard's work. Moroccan collections under the cork oak (Quercus suber) that were initially regarded as B. aereus, were described as a separate species—Boletus mamorensis—in 1978, on the basis of a rufous chestnut cap and a rooting stipe, or stem, with a reticulation often limited to the top (apex). However, molecular phylogenetic studies by Bryn Dentinger and colleagues in 2010, placed these collections very close to B. aereus, suggesting they are more likely an ecological variant or phenotype, rather than a distinct species. More recent phylogenetic studies by M. Loizides and colleagues in 2019, have confirmed that B. mamorensis is a later synonym of B. aereus, since collections identified as the two taxa could not be genetically separated and nested in the same clade. American mycologist Harry Thiers reported Boletus aereus from California in 1975; a taxonomic revision of western North American porcini boletes in 2008 formally established them as a separate species, Boletus regineus. These differ from B. aereus by nature of their more gelatinous cap skin (pileipellis), and belong in a different porcini lineage. Boletus aereus is classified in Boletus section Boletus, alongside close relatives such as B. reticulatus, B. edulis, and B. pinophilus. A genetic study of the four European species found that B. aereus was sister to B. reticulatus. More extensive testing of worldwide taxa revealed that B. aereus was sister to a lineage that had split into B. reticulatus and two lineages that had been classified as B. edulis from southern China and Korea/northern China respectively. Molecular analysis suggests that the B. aereus/mamorensis and B. reticulatus/Chinese B. 'edulis' lineages diverged around 6 to 7 million years ago. Bulliard gave Boletus aereus the common name of le bolet bronzé (the bronze bolete) in 1789, noting that it was called the cep noir (black cep) in other countries. It is commonly known as ontto beltza (black fungus) in Basque, porcino nero (black piglet) in Italian, and Cèpe bronzé in French. In Greek it is known as vasilikό (the royal one), or kalogeraki (little monk). The English common name is dark cep, while the British Mycological Society also approved the name bronze bolete.