First character donated a plant (5)
I believe the answer is:
agave
'a plant' is the definition.
(I know that Agave is a type of xerophyte)
'first character donated' is the wordplay.
'first' says to put letters next to each other.
'character' becomes 'a'.
'donated' becomes 'gave' (give can mean to donate).
'a' next to 'gave' is 'AGAVE'.
(Other definitions for agave that I've seen before include "Succulent; daughter of Cadmus" , "A cactus" , "plant in Mexico" , "Tropical plant" , "source of tequila" .)