Vegetative desiccation tolerance is a widespread but uncommon occurrence in plants. The majority of desiccation-tolerant plants are found in the less complex clades that constitute the algae and bryophytes. However, within the larger and more complex groups of vascular land plants there are some 120-130 species that exhibit some degree of vegetative desiccation tolerance. A phylogenetic look at vegetative desiccation tolerance reveals that this capability was lost during the time when tracheophytes first evolved and subsequently “re evolved” at least twelve separate times in various vascular plant lineages. The primitive mechanism of vegetative desiccation tolerance in the first land plants probably involved constitutive cellular protection coupled with active and inducible cellular repair, similar to that described for modern-day desiccation-tolerant mosses. Desiccation-tolerant angiosperms utilize an inducible cellular protection mechanism of tolerance that appears to derive from the programmed cellular protection mechanism seen in seeds. Desiccation-tolerant pteridophytes appear to employ a mechanism of tolerance that appears to have characteristics of both the primitive and the more recently evolved mechanisms seen in the angiosperms. Much of our evidence for this comes from the interpretation of a wealth of physiological data derived from the ecophysiology of Selaginella lepidophylla and a few desiccation tolerant ferns such as Polypodium polypodioides. However, detailed mechanistic studies have only been attempted using the desiccation-tolerant fern Polypodium virginianum so much still needs to be accomplished. Pteridophytes are in a unique position for the study of desiccation tolerance and its role in the evolution of the land plants and that with the availability of the modern tools of genomics the time is right for this area to expand.

Key words: desiccation tolerance, environment, evolution, pteridophytes, stress biology