Field, or meadow mushroom (Agaricus campestris). The edible field mushroom is one of about 60 species of Agaricus, a genus of gill fungi. The gills on the underside of the cap or pileus, contain the reproductive spore-bearing cells. Unlike plants, mushrooms (which are classified as part of the fungi kingdom) are not photosynthetic, but absorb food from the organic matter they live on or within. Agaricus bisporus, a close relative of the field mushroom, is the most widely commercially-cultivated mushroom.