Plant’s first appearance enthralling Henry (10)
I believe the answer is:
maidenhair
'plant's' is the definition.
(maidenhair is a kind of plant)
'first appearance enthralling henry' is the wordplay.
'first' becomes 'maiden' (as in a maiden voyage).
'appearance' becomes 'air' (both can mean an impression or character).
'enthralling' is an insertion indicator.
'henry' becomes 'H' (symbol for the unit of electrical inductance).
'maiden'+'air'='maidenair'
'maidenair' placed around 'h' is 'MAIDENHAIR'.
(Another definition for maidenhair that I've seen is " fern?".)