Leaf picked regularly from oldest herbs around (5)
I believe the answer is:
betel
'leaf' is the definition.
(I have seen 'Narcotic leaf' mean 'betel' so perhaps 'leaf' could also mean 'betel')
'regularly from oldest herbs around' is the wordplay.
'regularly from' indicates alternate letters (letters selected at regular intervals).
'around' shows that the letters should be reversed in order.
'oldest'+'herbs'='oldestherbs'
The alternate letters of 'oldestherbs' are 'leteb'.
'leteb' written backwards gives 'BETEL'.
'picked' acts as a link.
This may not be right. It may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for betel that I've seen before include "Dried leaf of a plant chewed in Asia as a mild stimulant" , "Palm with nuts for chewing" , "Plant leaf chewed in the East" , "Asian tree, whose nuts and leaves are chewed as a narcotic" , "Something stimulating" .)