SEM studies on vessels in ferns. 12. Marattiaceae, with comments on vesselpatterns in eusporangiate ferns

Scanning electron microscopy (SEM) of tracheary elements of roots of five s pecies from four genera of Marattiaceae and of the rhizome of one species r evealed vessel elements present in all. The secondary wall framework of per foration plates is the same as that of lateral wall pitting for vessel elem ents in all species. Thus, no specialization is present in perforation plat es of Marattiaceae compared to the simplified morphology of perforation pla tes of some leptosporangiate ferns (e.g., Dryopteridaceae, Polypodiaceae, a nd Pteridaceae). The difference between lateral wall pitting and perforatio n plates in tracheary elements of Marattiaceae cannot be seen by light micr oscopy (in which pit membranes are transparent), but is evident with SEM. D iversity in structure of perforation plates (especially the alternation of wide and narrow perforations within a plate) and presence of web-like pit m embrane remnants are evident. Vessels are widespread in both leptosporangia te and eusporangiate ferns, although specialization in perforation plates ( e.g., bars few and more widely spaced in lateral wall pitting of a given ve ssel element) is to be expected only in ferns of habitats with marked fluct uation in water availability. Vessels of Marattiaceae lack such specializat ions and are thus are correlated with the mesic habitats characteristic for the family.