Cellulose orientation in the outer epidermal wall of angiosperm roots: implications for biosystematics

The net orientation of cellulose fibrils in the outer epidermal wall of the root elongation zone of 57 angiosperm species belonging to 29 families was determined by means of Congo Red fluorescence and polarization confocal microscopy. The angiosperms can be divided in three groups. In all but four plant families, the net orientation of the cellulose fibrils is transverse to the root axis. Three families, the Poaceae, Juncaceae and Cyperaceae, have a totally different organization. In the root elongation zone of these plants, the net orientation of cellulose fibrils in the outer epidermal wall is parallel with the root axis. In roots of one family, the Arecaceae, an elongation zone in the literal sense of the word is absent and cellulose fibrils are randomly oriented.