The chestnut mushroom is not a species of its own but a marketing name — most often for the brown cultivated mushroom sold elsewhere as cremini, baby bella or brown cap, the young brown-skinned form of the same farmed species (Agaricus bisporus) that gives the white button and, grown on, the portobello. A firm, tan-to-chestnut-brown domed cap over pale gills that darken to chocolate as they ripen, it is prized in the kitchen for a deeper, nuttier, meatier savour than the mild white button while behaving exactly the same in the pan. In parts of the trade the same "chestnut mushroom" label is also pinned on an unrelated cultivated species, the true nameko-family Pholiota, so the name points to a colour and a flavour promise rather than to any one mushroom.