A bloomer in the field (9)

I believe the answer is:

buttercup

I'm a little stuck... Click here to teach me more about this clue!

'a bloomer' is the definition.
(plant which blooms)

I cannot understand how the remainder of the clue works.

(Other definitions for buttercup that I've seen before include "Common meadow flower" , "Common yellow flower" , "Common grassland plant, poisonous to livestock" , "weedy type" , "Bumboat woman" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.