trakeid

Trakeid is an elongated cell type in the xylem of vascular plants. In many texts the term is an alternative spelling of tracheid, a principal conduit for water transport and a contributor to mechanical strength in wood. Trakeids originate from tracheary elements during xylem development and mature as lignified, hollow cells with little cytoplasm remaining.

Structure and features: Trakeids are long, tapering cells with thick, lignified secondary walls. They communicate water mainly through bordered pits in their side walls; unlike vessel elements, they lack perforation plates, so conduction occurs via intercellular pits. Their ends overlap with neighboring trakeids to form a continuous conduit.

Function and distribution: The primary role is water transport from roots to shoots, and to provide mechanical support. Trakeids are especially important in gymnosperms, where vessels are scarce; in angiosperms, they may coexist with vessels, or be the dominant conductive element in some species, particularly in slow-growing or coniferous woods. Water movement through trakeids tends to be slower but can persist over long path lengths.

Terminology: The spelling “trakeid” appears in some texts as an alternative to “tracheid.” In current English botanical literature, “tracheid” is the standard form. The two terms are often used interchangeably, though modern usage generally adheres to “tracheid” when referring to xylem conducting cells. Related topics include xylem structure, bordered pits, and plant vascular evolution.