In a Thai-style tom kha kai, dill weed is not used, whereas in a Lao-style tom kha kai, dill weed (phak si, Lao: ຜັກຊີ) is used. Dill weed is a common herb which is used in Lao cuisine. The Thais' answer to dill weed (known in Thailand as phak chi Lao (Thai: ผักชีลาว), since it is known locally as a Lao herb) in Thai tom kha is coriander or cilantro (phak chi, Thai: ผักชี).
There are other versions of tom kha kai made with seafood (tom kha thale, Thai: ต้มข่าทะเล), mushrooms (tom kha het, Thai: ต้มข่าเห็ด), pork (tom kha mu, Thai: ต้มข่าหมู) and tofu (tom kha taohu, Thai: ต้มข่าเต้าหู้).
Ayusuk, S., Siripongvutikorn, S., Thummaratwasik, P., & Usawakesmanee, W. (2009). Effect of heat treatment on antioxidant properties of Tom-Kha paste and herbs/spices used in Tom-Kha paste. Kasetsart Journal Natural Science, 43(5), 305-312.
Buasi, J. Joy's Thai Food Recipe Cookbook. Apornpradab Buasi.
Sunanta, S. (2005, October). The globalization of Thai cuisine. In Canadian Council for Southeast Asian Studies Conference, York University, Toronto (pp. 1-17).