They illuminate gentle origins of some plants (5,5)

I believe the answer is:

light bulbs

'they illuminate' is the definition.

'gentle origins of some plants' is the wordplay.
'gentle' becomes 'light' (synonyms).
'origins of some plants' becomes 'bulbs' (many plants are grown from bulbs).
'light'+'bulbs'='LIGHT-BULBS'

I've seen this clue in The Guardian.

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