Cardamom
Green seed pods of a plant in the ginger family, with a cool, floral, resinous aroma.
Ground cardamom is in the spice aisle of most supermarkets, while whole pods are rarer there and cheaper and fresher from Asian or Middle Eastern grocers or by mail order. Whole pods keep their aroma far longer than the powder.
Substitute:
Ground cardamom can stand in for whole pods, about a quarter teaspoon for three to four pods, though it tastes flatter; no other spice matches the flavour, and smoky black cardamom is no substitute for green.