xylem secondary xylem Secondary xylem develops as part of secondary growth (GO:0080117). Secondary xylem is the wood of gymnosperm and dicot angiosperm trees, shrubs, and lianas. May be organized into axial (PO:0025410) and ray (PO:0025411) systems. Secondary xylem is often part of a shoot axis (PO:0025029) or a root (PO:0009005) but may occur in other organs. Some monocots have a primary thickening meristem (PO:0005039), located near the shoot apical meristem (PO:0020148), that gives the appearance of secondary growth and may produce lignified tissue that appears woody but is not composed of secondary xylem. Tracheary elements in secondary xylem (PO:0000290) have lignified cell walls with secondary thickening and are dead at maturity. secondary vascular tissue