cardamom
Green cardamom pods, whose small black seeds give a strong, floral, resinous aroma.
Whole green pods are sold in Asian, Turkish or Persian grocers and online; ordinary supermarkets often stock only ground cardamom. Ground cardamom loses its aroma quickly, so whole pods, crushed just before use, are worth seeking out.
Substitute:
Ground cardamom will do at a pinch, about a quarter teaspoon for three or four pods, but tastes flatter; black cardamom is no substitute, as it is smoky rather than floral.