Part of knoll, an open plain in South America (5)

I believe the answer is:

llano

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'plain in south america' is the definition.
'llano' can be an answer for 'plain' (I've seen this before). I'm not sure about the 'in south america' bit.

'part of knoll an open' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'LLANO' can be found hidden inside 'knoll an open'.

Can you help me to learn more?

(Other definitions for llano that I've seen before include "Flat area" , "Grassy plain in South?America" , "Treeless area" , "Treeless grassy plain in South America" , "(South American) grassy plain" .)

I've seen this clue in The Hindu.

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