Micro- and ultrastructural aspects of Norway spruce tracheids: A review

Norway spruce, Picea abies (L.) Karsten, is one of the most commercially important wood species in northern Europe. Wood from Norway spruce consists mainly (> 90%) of tracheids and the micro- and ultrastructure of these tracheids have a considerable effect on the wood, and its manufactured products. This literature review presents current knowledge on some important aspects of the micro- and ultrastructural morphology of Norway spruce tracheids. At the microstructural level, variation and general trends within the tree are given for tracheid length, tracheid diameter and cell wall thickness. At the ultrastructural level, the architecture of the secondary cell wall, and particularly its lamellation and microfibril orientation are considered. Where information on Norway spruce tracheids was lacking, tracheids of other conifers are reviewed. Thus, this review also gives an insight on the structure of other conifer tracheids since there are many similarities in structure between different conifer species.