Tree planted in California’s penitentiary (5)

I believe the answer is:

aspen

'tree' is the definition.
(aspen is a kind of tree)

'planted in california's penitentiary' is the wordplay.
'planted in' says the answer is hidden in the clue.
'ASPEN' can be found hidden inside 'californias penitentiary'.

(Other definitions for aspen that I've seen before include "city in Colorado" , "Tree, kind of poplar" , "Type of poplar" , "quill-like?" , "Its leaves flutter in the slightest breeze" .)

I've seen this clue in The Times.

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