Green grass, integrally, is salt-free starch (5,5)

I believe the answer is:

swiss chard

I'm a little stuck... Click here to teach me more about this clue!

'green' is the definition.
(I know that Swiss chard is a type of green)

'grass integrally is salt-free starch' is the wordplay.
I cannot quite understand how this works, but
'is' is within the answer.
This explanation may well be incorrect...

Can you help me to learn more?

(Another definition for swiss chard that I've seen is " Beet with edible leaves".)

I've seen this clue in the Sydney Morning Herald.

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