Button, cremini, and portobello are not three mushrooms but one species at three stages of maturity and two strains. The white button is the immature form of the common strain; cremini (baby bella) is a brown strain picked young; portobello is that same brown strain grown to full size, when the cap opens flat and the gills darken and concentrate. Flavor tracks age: a button is delicate and faintly sweet, a portobello is earthy, savory, and almost steak-like. As the most cultivated mushroom on earth it underpins everything from cream-of-mushroom soup to grilled portobello 'burgers'. Dry-sear hard to drive off the considerable water before browning.
Mild and clean when young, deep, earthy and meaty when full-grown.
Cultivated year-round in climate-controlled houses; no real season.
Identification is a chain of clues that must all agree. This is a reference, not an identification authority -- confirm every wild find with an expert.
Wild white Agaricus can be confused with deadly white Amanita. Amanita has a sac-like VOLVA at the base, a ring, and WHITE gills/spores; Agaricus gills turn pink then brown. Never forage white mushrooms without expert confirmation.
Cultivated and bought, not foraged. Pink-to-chocolate-brown gills and brown spore print; cap surface dry and smooth.