SEM studies on vessels in ferns. XV. Selected rosette epiphytes (Aspleniaceae, Elaphoglossaceae, Vittariaceae)

Tracheary elements from macerations of roots and rhizomes of Asplenium nidu s, Elaphoglossum hirtum, and Vittaria lineata were studied by means of SEM. All of these have perforation plates in tracheary elements of both roots a nd rhizomes. The perforation plates in roots and rhizomes show greatest dev elopment of perforations (perforations a little wider than pits of trachear y elements) in E. hirtum roots and rhizomes and least in V. lineata roots a nd in rhizomes of A. nidus (porose pit membranes in many perforations). The secondary wall framework of perforation plates is little different from th at of pitted wall areas in these three species. These rosette epiphytes hav e a lower degree of specialization of perforation plates that might accommo date rapid flow related to moisture availability fluctuations in comparison to perforation plates in vessels of rhizomatous epiphytic ferns. Generaliz ations are not warranted at this point, however. Rows of cushion-like struc tures occur adjacent to angles of the tracheary elements of E. hirtum. This is the first report of these in leptosporangiate ferns; they are known thu s far only in a eusporangiate fern, Danaea elliptica (Marattiaceae). Raised frames of wall material around perforations are newly reported for trachea ry elements of ferns in E. hirtum.