Plant is found across Rhode Island (4)
I believe the answer is:
iris
'plant' is the definition.
(type of flower)
'is found across rhode island' is the wordplay.
'found across' indicates putting letters inside.
'rhode island' becomes 'RI' (US postal abbreviation).
'is' going around 'ri' is 'IRIS'.
(Other definitions for iris that I've seen before include "Flag or flower in the eye" , "Greek goddess of the rainbow" , "Camera diaphragm" , "pupil's governor" , "Flag - part of eye" .)