trachéides

Trachéides, commonly called tracheids in English, are elongated, tapering cells that form a major component of the xylem in vascular plants. They function in the conduction of water and dissolved minerals and, in many plants, provide structural support.

Tracheids are typically long and narrow, with thick, lignified secondary walls. Water moves between adjacent tracheids mainly through bordered pits, which are specialized openings in the cell walls. Tracheids lack perforation plates; there are no openings that connect the lumen directly from one cell to the next, unlike vessel elements.

At maturity, most tracheids are dead cells with empty lumens and few organelles, a condition that minimizes resistance to water flow and reduces metabolic demand. They are formed by differentiation of xylem initials and become part of the secondary xylem as the plant wood develops, with secondary wall thickening following primary wall formation.

In terms of distribution, tracheids are present in all vascular plants, but they predominate in gymnosperms and many seedless vascular plants. Angiosperms often rely on vessel elements for rapid long-distance water transport, but tracheids remain important conductive elements in many angiosperms, especially in wood that requires support and resistance to embolism.

The wall thickenings can be annular, spiral, scalariform, or reticulate, reflecting taxon-specific patterns. Tracheids evolved early and are considered an ancient and conservative feature of vascular plants. Their simple, narrow design trades some conductive efficiency for greater mechanical strength and drought tolerance.