Epazote
A Mexican herb with jagged leaves and a sharp, resinous aroma reminiscent of camphor, mint and anise.
Caution: Use epazote only in the usual small seasoning amounts, as it is toxic in larger quantities and especially as an essential oil.
Epazote, also called Mexican tea or wormseed, is an herb from Central and South America whose leaves are used fresh or dried as a seasoning. Its flavour is idiosyncratic and strong: resinous, slightly medicinal, with notes of camphor, mint and anise that mellow during cooking and merge with the dish. In Mexico it belongs above all with black beans, in quesadillas, soups and salsas, and just a few leaves are enough. Fresh epazote is hard to find outside Latin American grocery stores; dried leaves are sold there and by mail order, and the plant grows easily from seed in a garden or on a balcony. Fresh epazote is considerably more aromatic than dried.
Substitute:
There is no real substitute, because no common herb has this resinous, camphor-like note. Mexican oregano with a little fresh coriander gives the dish an herbal touch but tastes different; often it is better simply to leave the herb out than to try to imitate it.