A portion of plant tissue (PO:0009007) that has as part a separation layer (PO:0006211) and a protective layer (PO:0006212), and is involved in the abscission (GO:0009838) of a fruit (PO:0009001), flower (PO:0009046), leaf (PO:0025034) or other plant structure (PO:0009011). [source: ISBN:047124529, POC:curators, POC:Laurel_Cooper]