Medicinal plant taken for Neptunian ends in salt water (5)
I believe the answer is:
senna
'medicinal plant' is the definition.
(I've seen this in another clue)
'neptunian ends in salt water' is the wordplay.
'ends' says to hollow out the word (remove centre letters).
'in' is an insertion indicator.
'salt water' becomes 'sea' (I've seen this before).
'neptunian' with its centre taken out is 'nn'.
'nn' put inside 'sea' is 'SENNA'.
'taken for' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for senna that I've seen before include "Leaf used as laxative" , "should make you want to go quickly" , "Tropical plant with medicinal leaflets" , "It produces pods" , "Its leaves are used medicinally" .)