Male viper in plant (6)
I believe the answer is:
madder
'plant' is the definition.
(madder is a kind of plant)
'male viper' is the wordplay.
'male' becomes 'm' (common abbreviation).
'viper' becomes 'adder' (adder is a kind of viper).
'm'+'adder'='MADDER'
'in' acts as a link.
(Other definitions for madder that I've seen before include "Made even more angry by the red dye" , "More angry or frantic" , "Dye-yielding plant" , "Plant; more angry" , "Angrier at the red colour" .)