The humble button mushroom belongs to a genus taxonomists still fight over
Agaricus gives the West its everyday supermarket mushroom and the wild field mushroom, but the genus is anything but simple. It holds more than 400 species, perhaps as many again disputed or newly found, including poisonous ones. Some prized relatives smell of marzipan, while others can soak up cadmium from polluted ground.
Its best-known members, the button mushroom Agaricus bisporus and its wild cousin A. campestris, lead Western mushroom cultivation. The field mushroom is the genus's type species; it is widespread across the northern temperate zone, grows in open grassland and has soft white flesh that stays white when cut. The genus name has several proposed origins, one linking it to an ancient people called the Agari who lived by a river and headland of similar names on the northern shore of the Sea of Azov.
Naming has been a long muddle. For years many books called these mushrooms Psalliota, from a Greek word for ring, a name Elias Fries published in 1821 for a tribe that Paul Kummer later raised to a genus. By the rules, splitting off the group containing the type should have forced the rest of the genus to be renamed, but that never happened, and proposals to settle the question formally have been judged unnecessary. Linnaeus's original use of the name is itself considered technically invalid.
DNA has reshaped the picture. Rolf Singer once divided the genus into 42 species in five sections, sorted by how the flesh reacted to air or chemical reagents and by subtle differences in shape; molecular analysis showed that scheme needed revising. By 2018 the genus was split into six subgenera and more than 20 sections, with much still to untangle.
One group centres on the horse mushroom, A. arvensis. Its members often grow in fairly dry places, bruise yellow or pinkish, and give off a sweet almond scent from benzaldehyde, which helps separate them from lookalikes. Many are highly valued as food, and A. subrufescens became a widely traded crop early this century under a tangle of names. Some species in the group accumulate cadmium and other toxins, so they are not always safe to eat.
Source: Agaricus
