Are and Portobello Mushrooms just large Crimini Mushrooms?

rutabeg..

As a fan of Portobello mushrooms, your question intrigued me as I was
not familiar with the Crimini variation of mushrooms.

You are correct in your assumption that the portobello (Agaricus
bisporus), also called portabella, is realted to the crimini.  As a
matter of fact, once a brown crimini mushroom grows to be 4 to 6
inches, it is then called a portabello.  Therefore, brown crimini
mushrooms can be considered a small portabello and portabellos are
large brown criminis

Thanks for your question and if you need any further clarification,
please let me know.

Regards,

-THV

Search Strategy:
portabello crimini

References:
Mushroom Council
http://www.mushroomcouncil.com/varieties/portobello.html

GourmetSleuth
http://www.gourmetsleuth.com/portobellosportabellas.htm