Clumsily, I step on it, a popular seasonal plant (10)
I believe the answer is:
poinsettia
'popular seasonal plant' is the definition.
(plant associated with Christmas)
'clumsily i step on it a' is the wordplay.
'clumsily' indicates anagramming the letters.
'i'+'step'+'on'+'it'='isteponit'
'isteponit' anagrammed gives 'poinsetti'.
'poinsetti'+'a'='POINSETTIA'
(Other definitions for poinsettia that I've seen before include "Plant with showy bracts, usu. red, pink or white" , "Flower popular at Christmas" , "Shrub often given at Christmas" , "poisonous bush" , "Ornamental house plant" .)