Desiccation-tolerance is the unique ability to revive from the air-dried state. In this review, I summarize the distribution of vegetative desiccation-tolerance within the land plants emphasizing bryophytes, and provide a current checklist of those moss, liverwort and hornwort species with documented and experimentally determined tolerance. Desiccation-tolerant species can survive equilibration with either modestly dry air (i.e., 70–80% RH or −30 to −48 MPa) or extremely dry air (i.e., 0–30% RH or less than −162 MPa), and have been identified within seven classes of bryophytes, the Andreaeopsida, Bryopsida, Polytrichopsida and Tetraphidopsida (mosses), Jungermanniopsida and Marchantiopsida (liverworts) and the Anthocerotopsida (hornworts); 210 out of 21,000 bryophyte species (ca. 1.0%) have been experimentally determined to possess vegetative desiccation tolerance—158 species of mosses, 51 species of liverworts and one species of hornwort. Finally, I propose a comprehensive survey of mosses, liverworts and hornworts using a standard procedure that employs modulated chlorophyll fluorescence for analyzing vegetative desiccation-tolerance (i.e., the “Austin Protocol”).

Bryophytes comprise the root from which the green plant Tree-of-Life developed. Molecular methods have been applied to a range of evolutionary problems in bryophytes including phylogenetic relationships among the major lineages, delimination of families and genera, infraspecific geographic patterns and speciation. This symposium encompasses molecular phylogenetic analyses at various levels of organization. Presentations include overviews of where we stand on resolving relationships within the three divisions: Bryophyta (mosses), Marchantiophyta (liverworts) and Anthocerophyta (hornworts). Other presentations address the evolution of development in early land plants, the use of characters describing gene and genome structure in phylogenetic analyses and infra-specific, geographically-correlated molecular variation in bryophytes.

Revolutionary new concepts of bryophyte relationships have emerged from molecular phylogenetic analyses conducted since the onset of the 21^st century. For example, sequence data contradict the historical notion that isophylly in leafy liverworts is plesiomorphic and that simple thalloid liverworts are monophyletic. Also contrary to traditional views are the concepts that Leiosporoceros is genetically distinct from other hornworts and that Oedipodium is sister to the peristomate mosses. Substantial increases in ultrastructural and anatomical data likewise have provided new insights on interrelationships. Because of this recent deluge in evolutionary studies on bryophytes, it is an opportune time to co-examine contemporary morphological knowledge and novel molecular hypotheses. An understanding of bryophyte evolution and biology is essential to identify structural innovations that accompanied early land colonization and to illuminate the evolution of more complicated body plans in tracheophytes. In this review, we examine the progress that has been made since the 1999 International Botanical Congress in clarifying the evolutionary history of the three groups of bryophytes. The state of our knowledge on interrelationships is discussed, with poorly-known, genetically divergent taxa illustrated for each group. Our review of bryophyte evolution includes a reëvaluation of the evolution of sperm cells, sporogenesis, stomata, symbioses, conducting cells and chloroplast ultrastructure in hornworts. We explore the prospects for future discoveries and advances with an emphasis on fundamental evolutionary problems that remain and the challenges that must be met to resolve them.

Molecular phylogenetic analyses of hornworts were performed on a nucleotide data set consisting of mitochondrial nad5, chloroplast rbcL and nuclear 18S gene regions. Thirty-seven hornworts representing most of the named generic segregates and morphological diversity in the group were sampled for the three gene analysis while an additional 25 samples were included in an analysis of rbcL alone. Results of these analyses confirm the relationships observed in prior molecular studies but also reveal a number of previously unrecognized yet highly supported clades. On the basis of this and continued morphological and ultrastructural investigations we propose a revised classification of the hornworts. At the highest levels, five well-supported clades are demonstrated and they include: 1) Leiosporoceros, which in most analyses is sister to the remaining hornworts; 2) Anthoceros, Folioceros and Sphaerosporoceros; 3) Notothylas and Phaeoceros; 4) Phymatoceros, a recently described genus that contains two species previously included in Phaeoceros; and 5) the remaining hornwort genera: Megaceros, Dendroceros, Nothoceros and a new genus, Phaeomegaceros. Challenges for continued studies that focus on hornwort systematics include obtaining live specimens worldwide and sorting through the chaotic taxonomy within the group. Morphological studies are hindered by poor preservation of existing collections, and the lack of background data and expertise in hornwort biology. Likewise, molecular sequence data are challenged by the deep divergences and potential effects of extensive RNA editing on phylogenetic reconstruction. Future directions for hornwort systematic studies include accumulating gene sequence data that resolve interspecific relationships and comparative anatomical/ultrastructural work that further elucidates biodiversity in the group. Our ongoing, interdisciplinary studies will culminate in a comprehensive analysis that combines molecular and morphological data for a total evidence approach.

Thalli of Nephroma arcticum were transplanted between and within a high-elevation alpine heath (1100 m) and a low-elevation subalpine mountain birch forest (380 m) in northern Swedish Lapland and harvested after eight years. Statistically significant differences (P < 0.05) were found between control samples for dark respiration rates, photon use efficiencies (apparent quantum yields) and light compensation points (all were higher in the high-altitude population). The following traits were significantly affected by transplanting: (1) epicortex thickness, (2) upper cortex thickness in the low-altitude population, (3) maximum photosynthetic rates, (4) dark respiration rates and (5) light compensation point. Of these malleable traits, all reduce the differences between the controls although there seems to be over-compensation in maximum net photosynthesis and under-compensation in dark respiration rate of the low-altitude population. Conservative traits, i.e., those that did not change significantly with transplantation were: (1) thallus thickness, (2) algal layer thickness, (3) algal cell diameter and (4) light saturation level. Small, yet significant differences in anatomy and physiology suggest that an ecotypic differentiation was established although the two internal transcribed DNA spacers ITS 1 and ITS 2 showed no corresponding variation between the populations.

We sampled epiphytic and ground macrolichens in three subtropical forest types in north-central Florida (sand pine scrub, longleaf pine and hardwood bottoms). We detected 101 macrolichen taxa during community surveys in the three subtropical forest types. We used nonmeteric multidimensional scaling to determine factors associated with gradients in lichen community composition. In addition, we evaluated diversity of macrolichen species and species groups among the three vegetation types. Gradients in lichen community composition were closely associated with differences in vegetation structure (canopy cover, percent evergreen conifers) of the three forest vegetation types. Sand pine scrub forests supported the richest diversity and highest abundances of macrolichens, despite the young age of the stands. Sand pine scrub stands were young due to the frequency of stand-replacing fires. Alpha diversity averaged 26 macrolichen taxa per plot, ranging from 12 species in the youngest longleaf pine stand to 51 species in a mature sand pine scrub stand. Ground lichen cover ranged from 0–82% and, when present, formed a mat from 5–14 cm thick. Longleaf pine stands lacked ground lichen cover due to their dense grass understory and high fire frequency. These stands also had lower diversities and abundances of epiphytic macrolichens. The hardwood bottom vegetation type is often flooded with water and lacks both a consistent vascular plant and ground lichen cover. Hardwood bottoms experience fire infrequently and are intermediate in canopy lichen diversity. We used Indicator Species Analysis to determine if macrolichen species associated more closely with one or more of the three subtropical forest types studied. Lichen species indicative of sand pine scrub communities include Bulbothrix confoederata, Cladina evansii, C. subtenuis, Cladonia prostrata, C. ravenelii, Crocynia pyxinoides, Parmotrema sulfuratum and Usnea dimorpha. Dirinaria picta, Heterodermia albicans, Leptogium cyanescens, Ramalina americana and Ramalina willeyi were indicative of hardwood bottoms, and no lichen species were consistently indicative of longleaf pine communities.

In northern Patagonia, macrolichens form species-rich and abundant epiphytic communities in southern beech forests. Five of the most abundant lichen species in the litter were selected in order to study mass loss rate and changes in mineral composition over time. The litter bag method was applied to the foliose lichens Pseudocyphellaria faveolata, Pseudocyphellaria flavicans, Nephroma antarcticum, Platismatia glauca and the fruticose Protousnea magellanica. Decomposition was measured over 550- and 600-day periods, starting in early and late summer, respectively. Mass loss after these periods varied from 30 to 82%. The decomposition rate between species differed from a half-life of 2.9 years in Pseudocyphellaria faveolata to 0.8 years in Protousnea magellanica and Plastismatia glauca. Samples deposited in early summer had a higher initial mass loss compared to samples deposited in late summer. After this initial loss, all species showed a similar temporal pattern with higher decomposition rates in winter and spring than in summer and fall. Pseudocyphellaria faveolata, Pseudocyphellaria flavicans and Nephroma antarcticum contain nitrogen-fixing cyanobacteria and had a considerably higher N concentration and lower C/N ratio than Platismatia glauca and Protousnea magellanica. However, the latter species had a faster mass loss. Changes in macronutrient concentrations were small apart from a rapid loss of P and K in Pseudocyphellaria spp. and increasing Ca and Mg concentrations in Platismatia glauca and Protousnea magellanica. We conclude that seasonal climatic variations partly control the decomposition pattern but that the time of litterfall strongly influences the initial decay rate.

Sphagnum atlanticum is distinguished from S. torreyanum by its well-enclosed branch leaf chlorophyll cells, less well-differentiated stem cortex, stronger brown pigmentation and a flatter capitulum. Sphagnum atlanticum also has falcate-secund branch leaves whereas those of S. torreyanum are straight.

A new Neotropical species of hornwort, Nothoceros superbus, is described from Costa Rica. The species is distinguished by its large size, strongly costate thallus with crispate-imperforate wings, dioicous condition and green, unicellular spores that are minutely papillose with tubercules dispersed on the borders and the distal face, and sometimes clustered in the center of the distal face. Nothoceros superbus has a combination of Megaceros-like spores and a Dendroceros-like thallus growth-form. The combination of these features supports its placement in the genus Nothoceros in the Dendrocerotaceae. Nomenclatural clarifications on Nothoceros endiviaefolius (Mont.) J. Haseg. and Nothoceros giganteus (Lehm. & Lindenb.) J. Haseg. are made. Based on new molecular and morphological data a new combination, Nothoceros canaliculatus (Pagán) comb. nov., is proposed.

The identity of three misunderstood and neglected cyanobacterial lichens from the southwestern United States is clarified based on type material studies. Anema dodgei is synonymous with Heppia despreauxii. Psorotichia segregata is identical with Lempholemma chalazanum. Psorotichia squamulosa belongs to the genus Gloeoheppia and the new combination Gloeoheppia squamulosa is proposed. The generic boundary between Gloeoheppia and Pseudopeltula is discussed and a key to the species of these two genera occurring in southwestern North America, Central America and the Caribbean is provided.

Bryophyte growth is most often cited as being primarily water-limited; however, experimental manipulation of water availability in the field has not previously been employed to test this hypothesis. Here we follow the growth responses of a leafy liverwort, Bazzania trilobata, to field water addition treatments. Our study system was an eastern hemlock stand located in the lower Hubbard Brook Valley in northern New Hampshire where Bazzania forms pure colonies over boulders. The experimental design accounted for effects of boulder treatment (control, water addition or water plus nitrogen), aspect (north- or south-facing), position (top, east or west side of a boulder) and liverwort stem density. To follow growth responses of Bazzania, we tracked changes in biomass gain, stem elongation and branching over 86 days. Environmental measurements for the evaluation period and supplemental physiological data for Bazzania were also taken. An increase in water availability did not evoke a straightforward increase in growth. Water and water plus nitrogen additions appeared to have a short-term initial effect on biomass gain and a moderating effect on elongation and growth rates. Biomass gain of Bazzania stems appeared limited by respiration costs, but further evidence would be needed to confirm this hypothesis. Branching was favored over stem elongation in grid cells with fewer stems and positions receiving higher light intensities. A carbon-balance hypothesis, considering the water, light and temperature conditions required to achieve a positive carbon balance, offers a more realistic model of the complexity of limitations to bryophyte growth. Comparative ecology of carbon balance for mosses and liverworts offers an intriguing and under-explored avenue in bryophyte ecology.

The secondary shoot elongation of Neckera pennata, a bryophyte vulnerable to forest management, was studied at three old-growth forest sites in Estonia for five years. Shoot elongation was significantly dependent on the Weather Index that was constructed on the basis of several weather parameters. For each shoot, the increments of adjacent years show significant autocorrelation. The mean shoot elongation during the study period was 2.8 mm per year. Although the species has been found mostly on Populus tremula in Estonia, it does not show a preference for this tree. The species' occurrence was significantly positively correlated with tree trunk circumference and bark pH. Seventeen percent of available tree trunks were occupied naturally on two ca. 1000 m² plots during the study period. Shoot transplantation at two sites was successful for 36% of shoots after four years and can be considered as a possibility for restoring populations of Neckera pennata.

Some controversy has existed concerning the relative levels of bryophyte species diversity in tropical and temperate areas. In this study global diversity patterns of pleurocarpous moss species are investigated by means of Nonmetric Multidimensional Scaling ordination based on checklists from 78 countries or other geographical areas spread over all the inhabitable parts of the world. By far, most of the diversity occurs outside the Holarctic area (excluding most of temperate eastern Asia), and especially the tropics have a very diverse pleurocarpous moss flora. Although earlier studies have shown that bryophyte alpha diversity is similar or almost similar in tropical and temperate areas, species turnover among pleurocarps is higher among areas within regions and especially among continents in the tropical rather than in the temperate zone. These results underline the priority of tropical areas for both research and globally sound conservation measures.

Frisch, Andreas, Klaus Kalb & Martin Grube. 2006. Contributions towards a new systematics of the lichen family Thelotremataceae. Bibliotheca Lichenologica 92: 1–556. J. Cramer in der Gebrüder Borntraeger Verlagsbuchhandlung, Berlin, Stuttgart, Germany. [ISBN 3-443-58071–8] Price € 88. Available from:  http://www.schweizerbart.de.

Lambley, Peter & Pat Wolseley (editors). 2004. Lichens in a Changing Pollution Environment. English Nature Research Report 525. 121 pages. Peterborough, U.K. Report may be obtained for free at:  http://www.english-nature.org.uk/pubs/publication/PDF/525.pdf

Schumacker, René & Jiří Váňa. 2005. Identification Keys to the Liverworts and Hornworts of Europe and Macaronesia (Distribution and Status), second edition fully revised and updated. Sorus, Poznań, Poland. [210 pp., 21 × 29 cm, ISBN 83-89949-11–34] Price: € 30 (Europe), $44 USD (Rest of the world). Available from: René Schumacker, rschumacker@ulg.ac.be; orders from Poland from Sorus Publishing & Printing House, Poznań, Poland,  www.sorus.pl.