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", "Tree with winged fruit", "maple tree", "Care about the maple?", "Plant", "Care about this tree", "ornamental tree", "Type of maple", "Maple tree" and "Tree or shrub of the maple genus".)