Crossword Genius

Vegetable product that could have made Cromwell unwell? (4)

Ross

I believe the answer is:

corm

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'vegetable product that could have made cromwell unwell?' is the definition.
The definition and answer can be both plants as well as being singular nouns.
Maybe there's an association between them I don't understand?

This is the entire clue.

Can you help me to learn more?

(Other definitions for corm that I've seen before include "Underground feature of crocus, gladiolus etc." , "Underground bulb-shaped stem" , "should eventually flower" , "Underground part of iris, crocus, etc" , "Underground part of, eg, cyclamen" .)

I've seen this clue in the Evening Standard.
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