To tantalise the left is a plant (6)

Here is my best explanation:

'plant' is the definition.
(teasel is a kind of plant)

'to tantalise the left' is the wordplay.
'to tantalise' becomes 'tease' (teasing is a kind of tantalizing).
'the left' becomes 'l' (common abbreviation).
'tease'+'l'='TEASEL'

'is a' acts as a link.