I'd never heard of chile de arbol, the author's favourite. I kept a score card of the number of recipes specifying particular kinds of chilies:
33x chile de arbol
12x serrano
2x urfa
1x each alleppo, marash & jalapeño
3x unspecified type (photo is of unknown variety from my cupboard)
I'm now checking for chile de arbol at any new market I'm in, since I'm curious about just how good it is. Any Litten chile experts?