SEM studies on vessels in ferns. 19. Marsilea

Tracheary elements from roots and rhizomes of M. drummondii, M. quadrifolia, and M. vestita supplement the work of other authors by showing features of Marsilea vessels not previously reported or not commonly reported. Pit dimorphism (wide pits lacking pit membranes alternating with narrow pits covered with pit membranes) form perforation plates in some vessel elements. Scalariform perforation plates with perforations like lateral wall pitting in size are common, and have not been previously reported in Marsilea by workers using light microscopy; further SEM studies may reveal such perforation plates to be more common in the family than presently thought. Circular to oval pits arranged in alternate, opposite, and transition fashion are characteristic of some vessels in the genus, as are tracheary element facets with few or no pits. The occurrence of perforation plates with few bars (found also in xeric and boreal ferns) and simple perforation plates in Marsilea may represent a capability for rapid uptake of water in habitats with relatively short periods of water availability.