innerbark

Innerbark is a botanical term describing the living tissues of a woody plant’s bark, principally the phloem, located outside the vascular cambium and inside the outer bark. In many species, innerbark comprises phloem tissue, which includes sieve elements or sieve cells, companion cells (in angiosperms), phloem parenchyma, and accompanying fibers. The vascular cambium lies adjacent to the innerbark on the inner side and generates new phloem toward the outside as the stem thickens. The primary role of innerbark is translocation: it distributes sugars and other nutrients produced in the leaves to roots, developing shoots, storage tissues, and reproductive organs. It can also participate in defense, storage of carbohydrates, and wound responses. In contrast, outer bark consists largely of dead protective tissues forming the rhytidome, produced by the cork cambium, and serves structural and protective roles. The term innerbark is sometimes used interchangeably with phloem, though phloem is the more precise anatomical term in many descriptions. The composition and arrangement of innerbark vary among plant groups; gymnosperm innerbark contains sieve cells rather than sieve elements, and supporting tissues differ from those in angiosperms. Understanding innerbark contributes to studies of tree physiology, forestry, and plant defense mechanisms.