From: The Cuisines of Mexico, by Diana Kennedy
The chile ancho is probably the chili most commonly used in Mexico. It is
the ripened and dried chile poblano, wrinkled and a deep reddish-brown color.
After soaking, it becomes a brick-red color. A large, good-quality ancho is
about 5 inches long and 3 inches wide, and it ranges from almost mild to
picante (hot). It is often stuffed. Toasted lightly and torn into small
pieces, it is used as a table sauce, or relish, but more often it is ground
to make the base of a cooking sauce. In Morelia it is confusingly called
pasilla, and I have seen it labeled pasilla in California.
This is a light-brown chile, with a wrinkled skin that smells distinctly
of smoke. It is in fact the chile jalapeno, ripened, dried, and smoked.
... Its name comes from the Nahuatl chil- ("chile") and poctli- ("smoke").
It can also be spelled chilpotle or chilpocle--all forms are used. The
average chile chipotle is 2 1/4 inches long and less than 3/4 inch wide.
It is very often used whole to season soups and stews, but is probably
most popular of all canned in vinegar or a red adobo sauce. The canned
ones are imported and available in all specialty stores carrying Mexican
There is no substitute for it.
As for Japanese chilis (often called jap peppers, which is easy to
confuse with jalapenos if you're not paying attention), these are a
variety developed by the Japanese which are pretty similar to anchos,
although usually smaller. They're also usually easier to get.