Made from whole, dried, chile de arbol chiles,de arbol powder can be hard to find. This powder adds a nice "heat" to sauces and rubs. You can substitute arbol powder in any any recipe that calls for cayenne pepper. You can read more about the arbol chile here including more substitutions and equivalents.
You can purchase this de arbol chile powder in our online store at Gourmetsleuth.com.
If you don't have de arbol powder, then the best substitute is: