Care about tree (4)
I believe the answer is:
Here is my best explanation:
'tree' is the definition.
(I've seen this in other clues)
'care about' is the subsidiary indication.
'about' indicates anagramming the letters.
'care' with letters rearranged gives 'acer'.
(Other definitions for acer that I've seen before include "Maple genus", "Care about this tree", "Maple tree", "Tree of maple family", "Tree or shrub of the maple genus", "Tree with winged fruit" and "Care about the maple?".)