Chili peppers may get all the attention, with their bright colors and flaming spiciness, but in my view the coriander plant is the real workhorse of Thai cuisine. Known as pak chee to the Thais, every part of the plant is used in Thai cooking. The green leaves of fresh coriander are often chopped up and sprinkled over soups and stir-fries, but they're more than just a garnish. Fresh coriander lends a very specific flavor to many dishes that wouldn't taste the same without it.
Fresh Coriander for sale
The most unique aspect of coriander's role in Thai cooking is the use of the root in many curry pastes. Ground fresh coriander root is probably the true "secret spice" in Thai cuisine. It's what gives Thai fried chicken that extra flavor and provides the undertone to dishes ostensibly flavored with garlic and pepper. The use of the root presents a problem for many cooks trying to master the true taste of Thai food, since most western supermarkets cut the roots off. Some solve this problem by growing the herb themselves.
Coriander seeds are perhaps the least used part of the plant in Thai cuisine. The small round seeds resemble white peppercorns, although not quite as hard. When called for, the seeds are usually dry roasted in a frying pan before being ground up as part of a curry paste.
Although most of the coriander used in Thai food is similar to that used elsewhere, another strain of coriander is sometimes called for. Known as pak chee farang or "foreigner coriander" in Thai, in English it's known as sawtooth coriander, understandably because of the herb’s long narrow grass-like blades with sawtooth edges.