Shrub with red or white flowers — unusually red alone (8)
I believe the answer is:
oleander
'shrub' is the definition.
(I've seen this before)
'unusually red alone' is the wordplay.
'unusually' is an anagram indicator.
'red'+'alone'='redalone'
'redalone' anagrammed gives 'OLEANDER'.
'with red or white flowers' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for oleander that I've seen before include "Adore Len (anag.)" , "No dealer in evergreen shrub" , "Evergreen flowering shrub from olden era" , "'Adorn eel, badly, with this shrub (8)'" , "No leader, oddly, for the flowering shrub" .)