Flowers one penny each, with powder inside (7)
I believe the answer is:
ipomoea
'flowers one penny each with powder inside' is the definition.
I can't tell whether this defines the answer.
'one penny each with powder inside' is the wordplay.
'one' becomes 'i' (Roman numeral).
'penny' becomes 'p' (short for pence).
'each' becomes 'ea' (abbreviation).
'with' is a charade indicator (letters next to each other).
'powder inside' becomes 'omo' (I am not sure about this - if you are sure you should believe this answer much more).
'ea' after 'omo' is 'omoea'.
'i'+'p'+'omoea'='IPOMOEA'
Can you help me to learn more?
(Other definitions for ipomoea that I've seen before include "Morning-glory genus" , "the morning glory" .)