Information found in most unusual ecosystem (10)
I believe the answer is:
rainforest
'ecosystem' is the definition.
(rainforest is a type of ecosystem)
'information found in most unusual' is the wordplay.
'information' becomes 'info' (synonyms).
'found in' means one lot of letters goes inside another.
'most unusual' becomes 'rarest' (I've seen this before).
'info' placed within 'rarest' is 'RAINFOREST'.
(Other definitions for rainforest that I've seen before include "geographical feature" , "has lots of tropical trees" , "Dense luxuriant tropical zone" , "area of ecological importance" , "high-growth area" .)