SEM studies on tracheids of lycopodiaceae; Observations on adaptations in phylloglossum

Scanning electron microscope (SEM) studies of stem and strobilus longisections of Huperzia, Lycopodium, and Phylloglossum were undertaken to explore ultrastructure of pit membranes in tracheids. The membranes do not characteristically have pores and may often lack evidence of cellulosic fibrils. Some pit membranes in Lycopodium did show cellulosic fibrils. Porose membranes were seen in some tracheids, an appearance probably related to scraping away of layers in pit membranes by the sectioning process, or in other cases, artifact formation. Metaxylem tracheids have wide borders on pits. Truly "reticulate" metaxylem tracheids are few. Protoxylem tracheids have helices with borders in Huperzia and Lycopodium, but in Phylloglossum protoxylem annuli and helices are non-bordered. Phylloglossum, which appears nested in Huperzia, lacks metaxylem and has numerous other adaptations to the distinctive ephemeral vernal bogs of Australia and New Zealand, similar to those in Droseraceae and Orchidaceae.