wild onions or leeks
韱 refers to wild onions or leeks, a type of pungent allium plant.
韱 combines 韭 (leek) with a phonetic component 㦰, suggesting a type of allium plant. The exact historical development is uncertain.
Inside 韱 is 韭 (leek), and the outer part 㦰 looks like a bundle of wild onions. Together they form a pungent wild allium.
For セン, imagine a field of wild onions sending up a strong scent: scent -> セン.