Baby Portobello mushrooms are similar in appearance to the Whites because they come from the same family (Agaricus). Look for a naturally light tan to rich brown cap and a very firm texture. They have a deeper, denser, earthier flavor than White mushrooms.

Among English speakers, Agaricus bisporus is known by many names. A young specimen with a closed cap and either pale white or light brown flesh is known as a button mushroom or white mushroom. When the flesh darkens, the immature mushroom is variously known as a crimini mushroom, baby portobello, baby bella, mini bella, portabellini, Roman mushroom, Italian mushroom, or brown mushroom. At this stage of maturation, the cap may also begin to open slightly. In maturity, it is called a portobello (frequently misspelled as portabello, or portobella). The French name is champignon de Paris ("Paris mushroom").