Alpha males upset by a single buttercup (7)
I believe the answer is:
anemone
'single buttercup' is the definition.
The definition and answer can be both plants as well as being singular nouns.
Maybe there's an association between them I don't understand?
'alpha males upset by a' is the wordplay.
'alpha' becomes 'a' (phonetic alphabet: alpha, bravo, charlie etc.).
'males' becomes 'men' (man is a kind of male).
'upset' shows that the letters should be reversed in order.
'by' means one lot of letters go next to another.
'a' becomes 'one'.
'men' back-to-front is 'nem'.
'a'+'nem'+'one'='ANEMONE'
Can you help me to learn more?
(Other definitions for anemone that I've seen before include "Plant; sea creature" , "Woodland plant, eg the windflower" , "Flower; marine polyp" , "White woodland flower" , "Buttercup-like flower or sea animal" .)