A tracheid is a non-living element of xylem formed from a single cell that serves to conduct water and to provide mechanical support. A tracheid is elongated, with tapering ends and thick, lignified (see lignin), and pitted walls. It is a long, empty, firm-walled tube running parallel with the long axis of the organ in which it lies, overlapping and in communication with adjacent tracheids by means of pits. Tracheids are characteristic of vascular plants other than flowering plants.