A portion of plant tissue at the interface between two plant structures, one of which is in a gametophyte development stage (PO:id) and one of which is in a sporophyte development stage (PO:id), and that has as parts transfer cells (PO:0000078). [source: ISBN:0716710072]
Comment
The transfer cells aid in nutrient transport. Examples include ovary placenta (PO:0020001) and fruit placenta (PO:0004535).