Tracheiden

Tracheiden, in botany often written as Tracheiden in German usage, refers to tracheids, elongated water-conducting cells that form a core part of the xylem in vascular plants. They are typically long, slender, and dead at maturity, with thick lignified secondary walls. Water and dissolved minerals move between tracheids primarily through bordered pits that connect adjacent cells, enabling vertical and some lateral transport.

Structure-wise, tracheids may show a range of wall thickening patterns, including annular, spiral, scalariform, or reticulate thickenings. Their tapered ends help them fit into the continuous, columnar xylem network. The presence of bordered pits, rather than perforation plates, distinguishes tracheids from vessel elements.

Functionally, tracheids provide both mechanical support and a conduit for water transport. They are found throughout vascular plants, but their prominence and role vary by lineage. Gymnosperms such as conifers rely heavily on tracheids for conduction and support, whereas many angiosperms retain tracheids alongside vessel elements, with vessels often handling the majority of rapid transport.

Development and evolution place tracheids among the oldest xylem elements. They originate from procambial cells in the developing vascular cylinder and mature through programmed cell death, leaving a lignified conduit. Vessel elements, which evolved later in many lineages, offer greater efficiency but are not universal.

Etymology and nomenclature: in German-language botany the term Tracheiden is used for tracheids; in English, the standard term is tracheid (plural tracheids).