Thai ingredients are plenfiful but one that is in almost all Thai dishes and every region of the country is nam pla (Thai น้ำปลา), a very aromatic and strong tasting fish sauce. Shrimp paste, a combination of ground shrimp and salt, is also extensively used.
Thai ingredients used in Thai dishes in the Central and Southern regions consist of a wide variety of leaves rarely found in the West, such as kaffir lime leaves (bai makrut, Thai ใบมะกรูด). The characteristic flavour of kaffir lime leaves appear in nearly every Thai soup (e.g., the hot and sour Tom Yum) or curry from those areas. It is frequently combined with garlic, galangal, lemon grass, turmeric and/or fingerroot (krachai), blended together with liberal amounts of various chillies to make curry paste. Fresh Thai basil is also used to add fragrance in certain dishes such as Green curry. Other typical ingredients include the small green Thai eggplants, tamarind, palm and coconut sugars, lime juice, and coconut milk. A variety of chilies and spicy elements are found in most Thai dishes.
Thai ingredients also include pak chee (cilantro or coriander), rak pak chee (cilantro/coriander roots), curry pastes, pong ka-ree (curry powder), si-yu dam (dark soy sauce), gung haeng (dried shrimp), pong pa-loh (five-spice powder), tua fak yao (long beans or yard-long beans), naman hoi (oyster sauce), prik Thai (Thai pepper), rice and tapioca flour, and nam prik pao (roasted chilli paste).
Thai ingredients don't actually include broccoli even though you will often see it used in Asian restaurants in the west in Phad Thai and rad na. It was never actually used in any traditional Thai food and is still rarely seen in the country. Usually, gailan is used.
Many thanks : Wikipedia; Thai Ingredients.