Plants fear of Brussels, say? That's about right (9)
I believe the answer is:
euphorbia
'plants' is the definition.
(euphorbia is the genus including spurge plants)
'fear of brussels say? that's about right' is the wordplay.
'fear of brussels say?' becomes 'EUphobia' (fear of the EU, which is based in Brussels).
'that's about' means one lot of letters goes inside another.
'right' becomes 'R' (common abbreviation).
'euphobia' going around 'r' is 'EUPHORBIA'.
(Other definitions for euphorbia that I've seen before include "flower" , "flowering plant" , "poinsettia" , "shrub" , "Plant of the spurge genus" .)