SEM studies on the vessels of heterophyllous species of Selaginella

Schneider, Edward L. and Sherwin Carlquist (Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, CA 93105). SEM studies on the vessels of heterophyllous species of Selaginella. J. Torrey Bot. Soc. 127:263-270. 2000. - Macerations of rhizomes of five species of Selaginella were studied with scanning electron microscopy (SEM). Although only tracheids were observed in two species of Selaginella (pit membranes thin or weblike but intact), vessel elements were seen in the remainder. Pit dimorphism resulting in intermittent perforation plates featuring wide perforations alternating with narrow pits occurs in S. lepidophylla. Highly porose pit membranes were observed in three species. Although the number of species examined is small, the apparent absence of vessels in some species and the absence of vessels with simple perforation plates are evidence that the heterophyllous species of Selaginella have xylem less xeromorphic than that of the homophyllous species; S. lepidophylla has more adaptations for potentially rapid conductive rates than other heterophyllous species. Structural features of vessels and tracheids of Selaginella as seen with SEM have also been reported in ferns.