Button, cremini and portobello are all the same mushroom at different ages
The white button mushroom, the brown cremini or chestnut, and the big flat portobello are one species, Agaricus bisporus, sold at different stages and colours. The white version did not exist commercially until 1925, when a Pennsylvania grower spotted a pale cluster sprouting in a bed of brown ones.
Agaricus bisporus grows wild in grasslands across Eurasia and North America, fruiting in autumn and winter on rich soil, compost and manure. The original wild form has a pale grey-brown cap with broad flat scales, domed at first and flattening to 5 to 10 centimetres. Its gills start pink, turn reddish brown and end up dark brown. Sold young and white, it may be called champignon de Paris; young and brown, it becomes chestnut or cremini; fully mature, with a cap of 10 to 15 centimetres, it is marketed as portobello, a name of disputed origin.
Growing it reliably took centuries. The French botanist Joseph Pitton de Tournefort gave the earliest scientific account of commercial cultivation in 1707. For a long time growers simply dug up mycelium from fields where mushrooms flushed well and replanted it in composted manure, a method that also transplanted diseases. In 1893 the Pasteur Institute in Paris produced sterilised pure-culture spawn for horse-manure compost, removing much of the guesswork.
Commercial strains were originally light brown. In 1925, Louis Ferdinand Lambert, owner of the Keystone Mushroom Farm in Coatesville, Pennsylvania, and a trained mycologist, found white mushrooms growing among his brown crop and took them to his lab. Like white bread, the pale version struck shoppers as more appealing and spread widely. Today the species is cultivated in more than 70 countries.
Nutritionally, the mushroom is 92 percent water with little fat, and 100 grams supply only 22 kilocalories along with plenty of riboflavin, niacin and pantothenic acid. Its vitamin D content is tiny when fresh, but exposure to ultraviolet light boosts it more than fiftyfold. Wild lookalikes exist. Young destroying angels, lethal Amanita mushrooms, look similar but have a cup at the base and pure white gills, while the inedible Agaricus xanthodermus smells of phenol and turns yellow when bruised.
Source: Agaricus bisporus
