Phloem

Article By:

Walsh, Michael A. Department of Biology, Utah State University, Logan, Utah.

Last reviewed:January 2021

DOI:https://doi.org/10.1036/1097-8542.507200

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• Phloem, published June 2014:Download PDF Get Adobe Acrobat Reader

The principal food-conducting tissue in vascular plants. The long-distance transport of nutrients in plants occurs in the phloem, which is a highly specialized tissue that links all the organs of the plant. The conducting cells of phloem are known as sieve elements (Fig. 1), but phloem may also include companion cells, parenchyma cells, fibers, sclereids, rays, and certain other cells. As a vascular tissue, phloem is spatially associated with xylem (the water-conducting tissue), and the two together form the vascular system. Less is known of phloem than of xylem, partly because of its lesser direct economic importance and partly because the sieve elements function for a short time (usually one season) and then undergo marked structural and functional changes, such as crushing or sloughing off as a result of periderm formation in the case of woody plants. See also: Parenchyma; Periderm; Phloem loading; Plant anatomy; Plant mineral nutrition; Plant physiology; Plant primary vascular system; Plant tissue systems; Xylem

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