Flower girl regularly seen in Tyneside (4)
I believe the answer is:
nile
'flower' is the definition.
(Nile River is an example)
'girl regularly seen in tyneside' is the wordplay.
'regularly seen' indicates alternate letters.
'in' indicates putting letters inside.
'tyneside' becomes 'ne' (region in North East of England).
The alternating letters of 'girl' are 'il'.
'il' going into 'ne' is 'NILE'.
(Other definitions for nile that I've seen before include "River associated with Cleopatra" , "River that's Blue and White" , "World's longest river" , "'The longest river, blue and white (4)'" , "River of eastern Africa" .)