Maslova, E.V., Yu.V. Mosseichik, I.A. Ignatiev, O.V. Ivanov & M.S. Ignatov. On the leaf development in Palaeozoic mosses of the order Protosphagnales
Arctoa (2012) 21: 241-264
Upper Palaeozoic mosses of the order Protosphagnales are studied for their leaf development and found to be quite different from modern mosses. In the latter, the small actively dividing cells occur at latest stages of leaf development in the proximal part of leaf, whereas in Protosphagnales cell divisions may continue in the subapical part of leaf. Also, zones of small cells occur in some genera in the median part of the leaf, indicating relatively independent development of different leaf parts. The narrow insertion of leaves, which consists almost entirely of the costa, makes easier late growth of the basal leaf portion, where expanded aurucules may form. The small cells in median part of leaf differentiate both acropetally and basipetally, but cells above this zone become dimorphous more often than below it. The pattern of cell dimorphism is correlated with shifts of cell rows during leaf development.