A multi-tissue plant structure (PO:0025496) that is a functional unit, is a proper part of a whole plant (PO:0000003), and includes portions of plant tissue (PO:0009007) of at least two different types that derive from a common developmental path.

Examples include stem (PO:0009047), leaf (PO:0025034), and root (PO:0009005). May include individual plant cells (PO:0009002) that are not part of a portion of plant tissue (e.g., idioblasts, PO:0000283). A plant organ may have one or more different plant organs as parts, such as a sporophyll (PO:0009026) that may have as part a sporangium (PO:0025094) or a carpel (PO:0009030) that may have as part a plant ovule (PO:0020003).