Bit of flower that's not wild kept in tin (6)
'bit of flower' is the definition.
('stamen' is part of 'flower')
'not wild kept in tin' is the wordplay.
'not wild' becomes 'tame' ('tame' is the opposite to 'wild').
'kept in' indicates putting letters inside.
'tin' becomes 'sn' (Sn is the chemical symbol for tin).
'tame' put inside 'sn' is 'STAMEN'.
'that's' is the link.
(Other definitions for stamen that I've seen before include "Flower pollen carrier", "Manet's (anag.)", "Bit of a bloomer", "Fertiliser", "Section of a flower".)