Petitions about a floral decoration (10)
I believe the answer is:
poinsettia
'floral decoration' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'petitions about a' is the wordplay.
'about' is an anagram indicator.
'petitions' with letters rearranged gives 'poinsetti'.
'poinsetti'+'a'='POINSETTIA'
Can you help me to learn more?
(Other definitions for poinsettia that I've seen before include "bloom" , "Shrub often given at Christmas" , "poisonous bush" , "Plant with showy bracts, usu. red, pink or white" , "American plant" .)