Radhuni is the dried fruit of Trachyspermum roxburghianum, a small annual of the carrot family grown in the eastern Indian subcontinent and mainland Southeast Asia. Barely a millimetre or two long, the ridged greenish-brown seeds smell sharply of celery and parsley — clean, green and slightly bitter — and are a defining note of Bengali cooking, where they are fried whole in hot oil to release a savoury, herbaceous aroma. Though endlessly confused with ajwain and with true celery seed, radhuni is a distinct spice with its own persistent, almost soapy-green pungency.