White mushrooms (Agaricus bisporus), also called button mushrooms, are the pale, immature form of the same species sold as brown cremini mushrooms and, at full maturity, as portobello mushrooms; the differences in color, size, and flavor intensity come from age and strain, not a different species.
Cultivated commercially in France since the 17th century, white mushrooms are now grown worldwide, with the US, China, and the Netherlands among the largest producers, typically in climate-controlled facilities rather than in the wild.
They're used sautéed, roasted, or grilled as a side, or added to soups, stews, and sauces, where their mild flavor takes on other ingredients in the dish. Their taste is earthy, savory, and slightly nutty, pairing well with thyme, rosemary, parsley, garlic, onions, shallots, and dairy like cream, cheese, and butter. They're low in calories and a source of vitamin D, B vitamins, and selenium.