Agaricus brunnescens

About

Agaricus bisporus, the cultivated mushroom, is a basidiomycete mushroom native to grasslands in Eurasia and North America. It is cultivated in more than 70 countries and is one of the most commonly and widely consumed mushrooms in the world. It has two color states while immature – white and brown – both of which have various names, with additional names for the mature state, such as chestnut, portobello, portabellini, button, cremini, and champignon de Paris.

Summary from Wikipedia