chiles de arbol means: Treelike; Chile de Rbol; thin and small; 2 to 3 inches long, including stems. It is usually ground to a powder to be used in chile sauces. They go well with tomatoes and other citrus fruits, as well as herbs like rosemary and oregano. Common Mexican names include pico de pajaro bird’s beak, and cola de Rat’s Tail. (in Cooking Dictionary)