Trachyspermum roxburghianum (D. C.) Craib
[synonyms T. involucratum Wolff non Marie, Carum roxburghianum Benth ex Kurz]

Umrao Singh, A. M. Wadhwani, B. M. Johri, "Dictionary of Economic Plants in India"
Indian Council of Agricultural Research, 1983 (2nd Ed)

Ajwain: Trachyspermum ammi

Radhuni: Trachyspermum roxburghianum

Celery seed: Apium graveolens

 

A completely unscientific survey suggests that 3 out of 5 people (the total number surveyed) think that Radhuni tastes most like Ajwain (I was one, and the only person who was biased by the knowledge that the two supposedly belong to the same genus).  I think that it tastes more like Methi (the legume seed fenugreek, Trigonella foenum-graecum) than anything else.

Intriguing thought: This makes it the fruit of the salad leaf I encountered recently, pak chi lom*, which my botanist colleague in Thailand identified as Trachyspermum roxburghianum. Makes sense then that radhuni would be something that people from East, but not West, Bengal add to their panch-phoron...

*As also identified here.