They may be prickly, caught in problematic activity (5)

I believe the answer is:

cacti

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'they may be prickly caught' is the definition.
The definition suggests an adverb but the answer is not.

'in problematic activity' is the wordplay.
'in' indicates a hidden word.
'CACTI' is hidden within 'problematic activity'.

Can you help me to learn more?

(Other definitions for cacti that I've seen before include "they shoot in the desert" , "Prickly plants" , "growing group" , "Plants native to arid regions" , "Features of westerns" .)

I've seen this clue in The Telegraph.

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