Still-life by Van Gogh one mounts (6)

I believe the answer is:

irises

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'still-life by van gogh' is the definition.
I can't tell whether this defines the answer.

'one mounts' is the wordplay.
'one' becomes 'i' (Roman numeral).
'mounts' becomes 'rises' ('rise' can be a synonym of 'mount').
'i'+'rises'='IRISES'

Can you help me to learn more?

(Other definitions for irises that I've seen before include "Plants with sword-shaped leaves" , "Coloured membranes in eyes, or showy flowers" , "Subject for van Gogh" , "Parts of eyes or flowering plants" , "Flowers painted by Van Gogh" .)

I've seen this clue in The Guardian.

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