Claim to be wild asters (6)
I believe the answer is:
assert
'claim' is the definition.
(I know that claim is a more specific form of the action assert)
'wild asters' is the wordplay.
'wild' indicates an anagram.
'asters' with letters rearranged gives 'ASSERT'.
'to be' is the link.
(Other definitions for assert that I've seen before include "Maintain - allege" , "protest" , "Affirm, allege" , "State firmly and with conviction" , "State firmly, declare as true" .)