immature and white 
AKA: common mushroom, button mushroom, white mushroom, button mushroom, cultivated mushroom, table mushroom, and champignon mushroom or champignon

immature and brown
AKA: Swiss brown mushroom, Roman brown mushroom, Italian brown mushroom, cremini/crimini mushroom, and baby bella

mature 
AKA: portobello mushroom, portabella mushroom, and portobella mushroom

Family: Agaricaceae

Fungus