Grain, bivalve mollusc, and roadside plant (10)

I believe the answer is:

corncockle

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'roadside plant' is the definition.
The answer and definition can be both plants as well as being singular nouns.
Maybe there's an association between them I don't understand?

'grain bivalve mollusc' is the wordplay.
'grain' becomes 'corn' (corn is a kind of grain).
'bivalve mollusc' becomes 'cockle' (I've seen this before).
'corn'+'cockle'='CORNCOCKLE'

'and' acts as a link.

Can you help me to learn more?

I've seen this clue in The Times.

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