Woodlouse, perhaps, one by flower in turf (6)
I believe the answer is:
isopod
'woodlouse perhaps' is the definition.
(woodlouse is a kind of isopod)
'one by flower in turf' is the wordplay.
'one' becomes 'i' (Roman numeral).
'by' means one lot of letters go next to another.
'flower' becomes 'po' (Italian river).
'in' indicates putting letters inside.
'turf' becomes 'sod' ('sod' can be a synonym of 'turf').
'po' inserted into 'sod' is 'sopod'.
'i'+'sopod'='ISOPOD'
(Other definitions for isopod that I've seen before include "Member of an order of crustaceans" , "small crustacean" , "Crustacean with seven pairs of legs for crawling" , "Woodlouse, say" , "Slater, for instance" .)