SEM studies on vessels in ferns. x. selected Osmundaceae and Schizaeaceae

Vessel elements in the putatively primitive leptosporangiate fern families Osmundaceae and Schizaeaceae have scalariform secondary-wall framework alike on end wall and lateral wall. Only by means of scanning electron microscopy (SEM) can presence or absence of pit membranes be demonstrated, and thus vessels have not hitherto been claimed for these two families. Criteria for designating perforations include pits transitional between lateral wall pits and conventional perforations in which porosities of various sizes occur in pit membranes, indicating partial lysis of the primary wall. Vessels occur in both roots and rhizomes of the examined species. In Schizaeaceae, wide perforations alternating with narrow pits occur in perforation plates of some vessels. Although vessels with specialized end walls occur in a few ferns of ecological sites with strongly marked fluctuations in water availability, less specialized vessels occur in a range of ferns of mesic habitats, as shown by Todea (Osmundaceae), Anemia (Schizaeceae), and Lygodium (Schizaeaceae). The vessel elements of these species of Osmundaceae and Schizaeaceae are compatible with the near-basal position among leptosporangiate ferns commonly accorded these families.