Diverse algae possess the ability to recover from extreme desiccation without forming specialized resting structures. Green algal genera such as Tetradesmus (Sphaeropleales, Chlorophyceae) contain temperate terrestrial, desert, and aquatic species, providing an opportunity to compare physiological traits associated with the transition to land in closely related taxa. We subjected six species from distinct habitats to three dehydration treatments varying in relative humidity (RH 5%, 65%, 80%) followed by shortand long-term rehydration. We tested the capacity of the algae to recover from dehydration using the effective quantum yield of photosystem II as a proxy for physiological activity. The degree of recovery was dependent both on the habitat of origin and the dehydration scenario, with terrestrial, but not aquatic, species recovering from dehydration. Distinct strains of each species responded similarly to dehydration and rehydration, with the exception of one aquatic strain that recovered from the mildest dehydration treatment. Cell ultrastructure was uniformly maintained in both aquatic and desert species during dehydration and rehydration, but staining with an amphiphilic styryl dye indicated damage to the plasma membrane from osmotically induced water loss in the aquatic species. These analyses demonstrate that terrestrial Tetradesmus possess a vegetative desiccation tolerance phenotype, making these species ideal for comparative omics studies.

A new species of Tetradesmus (Tetradesmus adustus) is described from desert soils of southwestern North America. The identification is based on phylogenetic analysis of data from nuclear (ITS2 rDNA) and plastid (rbcL, tufA) barcode markers. This newly described species represents the fifth cryptic species of arid-adapted algae in Scenedesmaceae. A re-analysis of published sequences attributed to desert Tetradesmus in the context of our newly obtained data reiterates the importance of robust phylogenetic analysis in identification of cryptic taxa, such as species of Tetradesmus.

Diverse algae possess vegetative desiccation tolerance, the ability to recover from extreme desiccation without forming specialized resting structures. Green algal genera such as Tetradesmus (Sphaeropleales, Chlorophyceae) contain both terrestrial and aquatic species, providing an opportunity to compare physiological traits associated with the transition to land in closely related taxa. We subjected six species from aquatic and terrestrial habitats to three desiccation treatments varying in final relative humidity followed by short-and mid-term rehydration. We tested the capacity of the algae to recover from desiccation using the effective quantum yield of photosystem II as a proxy for physiological activity. The degree of recovery was dependent both on the habitat of origin and the desiccation scenario, with terrestrial, but not aquatic species, recovering from desiccation. Distinct strains of each species responded similarly to desiccation and rehydration, with the exception of one aquatic strain that recovered from the mildest desiccation. Cell ultrastructure was uniformly maintained in both aquatic and desert species during dehydration and rehydration, but staining with an amphiphilic styryl dye indicated desiccation-induced damage to the plasma membrane in the aquatic species. These analyses demonstrate that terrestrial Tetradesmus possess the vegetative desiccation tolerance phenotype, making these species ideal for comparative omics studies.