A portion of secondary xylem (PO:0005848) that lacks living secondary xylem parenchyma cells (PO:0004525). [source: ISBN:0471245208, POC:curators]
Comment
Heartwood has ceased to function in storage and conduction, and the reserve materials have been removed or converted into heartwood substances. It is generally darker colored than sapwood (PO:0004513) and is found in the center of a shoot axis (PO:0025029) or root (PO:0009005), interior to the sapwood. Heartwood forms at the end of a cell death stage of secondary xylem (PO:0025466).