SEM studies on vessels in ferns. 6. Woodsia ilvensis, with comments on vessel origin in ferns

Woodsia ilvensis has a range of degrees of specialization in perforation plates of vessel elements in roots, but as a whole they are somewhat more specialized than those of W. scopulina, and much more specialized than those of W. obtusa. Rhizomes of W. ilvensis have vessel elements with only moderate degrees of specialization in perforation plates. Woodsia ilvensis has lateral wall perforation plates well defined on root vessel elements, less well defined ones in rhizomes. These expressions also occur in W. scopulina, whereas W. obtusa lacks lateral wall perforation plates. The more highly specialized perforation plates of W. ilvensis roots may relate to the more highly seasonal habitats: it occurs in high latitudes and altitudes, and likely experiences more cold than W. scopulina (from intermediate habitats) and W. obtusa (from less extreme habitats). Lateral wall perforation plates are, as far as known, unique to ferns, and may related to vessel grouping in steles, and to minimal division of labor among tracheary elements in vessel-bearing ferns.