paraxyleeni

Paraxylem is a term used in plant anatomy to describe part of the primary xylem tissue in the vascular cylinder (the stele). It refers to xylem elements that differentiate after the protoxylem but before the metaxylem during primary growth. Paraxylem is typically located adjacent to the protoxylem within the developing stem or root, and its arrangement can vary among plant groups.

Paraxylem elements are tracheary elements, such as tracheids or vessels, with thickening patterns that may be annular, helical, or scalariform. In many species, paraxylem forms in radial files or as distinct strands around the protoxylem and may be partly transient, becoming modified or replaced as the metaxylem differentiates and enlarges. In other cases, paraxylem contributes to the mature xylem alongside metaxylem rather than being wholly transient.

Functionally, paraxylem participates in the conduction of water and dissolved minerals during early vascular development. As the plant matures, metaxylem typically assumes a greater role in water transport due to its larger elements and enhanced efficiency, while paraxylem can become less prominent or incorporated into the mature xylem network.

Taxonomy and terminology vary by author; the concept is mainly used in comparative anatomy and historical descriptions of primary xylem organization. The term paraxylem emphasizes its position beside the protoxylem and its developmental relationship to other xylem types.