Learner at university in bloomer (5)
I believe the answer is:
Here is my best explanation:
'bloomer' is the definition.
(I've seen this before)
'learner at university in' is the wordplay.
'learner' becomes 'l'.
'at university' becomes 'up'.
(Other definitions for lupin that I've seen before include "Flower called after wolf", "Plant with erect spikes of usually purplish-blue flowers", "Pod-producing garden flower", "something flowery", "Garden plant of the pea family", "Pea relative with tall spikes of flowers", "It has tall flower spike", "Nobody's child", "Flowering plant" and "Nil up in this flower".)