Reptile cultivated tartan leeks (11)
I believe the answer is:
rattlesnake
'reptile' is the definition.
(type of snake)
'cultivated tartan leeks' is the wordplay.
'cultivated' is an anagram indicator.
'tartan'+'leeks'='tartanleeks'
'tartanleeks' is an anagram of 'RATTLESNAKE'.
(Other definitions for rattlesnake that I've seen before include "Serpent with noisy tail" , "Venomous creature" , "Creepy type" , "Virulent type" , "Sidewinder" .)