Katahdin, the highest peak in Maine at 1606 m, has about 13 km² (1300 ha) of alpine and subalpine tundra and krummholz on a summit plateau and in upper cirque basins. Lichens and bryophytes have been collected above tree line since the mid-19^th century, but the cryptogam biota of the mountain has remained incompletely documented. For 16 days during 2001–2004 we inventoried lichens and bryophytes of the subalpine and alpine zones of Katahdin (above 884 m), visiting open alpine tundra, alpine cliffs in glacial cirques, seeps, fellfields, krummholz and subalpine forests. We relocated most species represented by historic collections and added many more to the documented biota, including significant range extensions and species new to North America or northeastern United States. The floristic results are presented in two associated papers. Here we (1) summarize previous studies of the botany, ecology and geology of Katahdin; (2) compare quadrats from a Diapensia heath in exposed alpine tundra on the Table Land with a snow bed community just below the Table Land, where a marked difference in the bryophyte and lichen assemblages may reflect cryptogam-vascular plant interactions and/or site-specific differences; and (3) summarize unpublished weather data collected at the Chimney Pond Ranger Station (ca. 890 m). Katahdin and Mt. Washington, New Hampshire, have similar recent temperature and precipitation records on the basis of the available data. Katahdin shares some vegetation components and climate features with mountain ranges in the Pacific Northwest, New Zealand and the Scottish Highlands that have been studied for lichens and/or bryophytes.

A total of 293 different lichens (and lichenicolous fungi) were found above an elevation of 884 m on Katahdin during fieldwork from 2000 to 2004 and from study of previously collected herbarium specimens. Thirteen of these are new to North America, 39 additional lichens are new to northeastern United States and 26 additional ones are new to Maine; three additional taxa are almost certainly new to science but are not formally described in this study. We identified eight distinct lichen habitats on Katahdin: (1) A1, exposed alpine tundra and fellfields; (2) A2, high elevation alpine sites protected from northwest winds; (3) A3, east-facing alpine late-snow areas; (4) A4, alpine krummholz; (5) A5, cirque headwalls facing east and north; (6) A6, cirque headwall facing southeast; (7) B1, exposed low-altitude tundra, talus and krummholz; and (8) B2, subalpine forests. Each habitat except A4 had numerous lichens (10–56 taxa) found in none of the others, and each differed statistically from two to six other habitats by a quantitative measure of the Arctic-boreal-temperate (ABT) distribution of its lichens. Habitat A3 had, on average, the most Arctic lichens, followed by A1, A2, A5, B1, A6 and A4, with B2 having the fewest Arctic lichens and the most with a temperate distribution. Lichen ABT values for the eight habitats are well predicted (R²  =  96.9%) by a multiple regression equation incorporating three independent variables: average elevation above sea level of the lichens collected in a habitat class; an estimate of solar gain for each of the eight habitats; and the presence or absence of trees (including krummholz). We compared our results with those for Mt. Albert, Gaspé, Quebec, the only other comprehensive study of alpine lichens in northeastern North America, for such parameters as species presence/absence, substrata and ABT value. We suggest that future studies looking into effects of global warming or increases or decreases in air pollution will be facilitated by the study of certain habitats rather than the entire alpine and subalpine Katahdin region.

Field studies on the east side of Mount Katahdin, Maine, from 2001 to 2004, and an appraisal of published and unpublished Katahdin records from previous work documented 203 different bryophytes (131 mosses and 72 liverworts) for subalpine conifer forest, alpine tundra and cirque walls, and krummholz in between. This work represents the only recent investigation of a high altitude bryoflora in the mountains of the northeastern United States. Two mosses (Hygrohypnum smithii, Pohlia tundrae) are new to this region, and six others, including Neckera oligocarpa, are new records for Maine. Investigations of Grimmia (4 spp.), Cynodontium (2 spp.) and Kiaeria (2 spp.) clarified the application of taxonomic concepts for these mosses relative to previous published work. In conjuction with parallel studies of Katahdin lichens, eight habitats were specified for the study area. These habitats were largely the same places as those recognized for lichens. The eight habitats differed in the number of Arctic mosses and in unique occurrences of various mosses and liverworts. Mean Arctic-boreal-cool temperate values, introduced as an analytical tool to evaluate the distributional affinities of Kathadin lichens, were calculated for bryophytes for seven of eight habitats. The mean for each habitat class was well predicted by a multiple regression equation, with altitude, solar gain and snowpack persistence, but not substratum, as independent variables. Upper and lower altitutinal limits of bryophyte species occurrence were determined. The documented presence of Katahdin alpine bryophytes in four other mountain areas in northeastern United States and adjacent Québec, Canada, showed fewer of them in western areas (the high Adirondack Mountains, New York and Mt. Mansfield, Vermont), a possible outcome of increasing oceanic conditions eastward.

Habitat segregation between two closely related Pohlia species, P. annotina and P. drummondii, was documented on the basis of field observations at higher elevations in Yakushima Island, supplemented with molecular analysis to confirm the species identities. Both species, belonging to the P. annotina complex, grow on bare soils and have similar gametophytic features as well as heavy dependence on asexual reproduction by propagules produced in leaf axils. The species show a clear difference in habitat preference: P. drummondii is strictly confined to invariably wet or moist soils such as at the edge of bog swamps or streamlets in mountain trails excavated by heavy rains, while P. annotina is mostly found in less humid habitats even if both species sometimes grow side-by-side. A phylogenetic tree using rbcL sequences confirmed that P. annotina, P. drummondii and P. flexuosa, another member of the complex, represent distinct species. In addition to the usual vermicular propagules, Japanese plants of P. annotina and P. flexuosa were shown for the first time to have several other kinds of propagules, as also found in European and American plants. Morphological changes during propagule development in Japanese P. drummondii are also reported.

Compared to the mainland, boreal oceanic islands would be expected to have a depauperate lichen biota because of their isolation, small area, exposure to salt spray and structurally simple habitats. We surveyed the macrolichens (non-crustose lichens) and quantified habitat associations on Kent Island, an 80-hectare island that lies at the mouth of the Bay of Fundy, New Brunswick, Canada. A total of 43 species in 13 genera were identified, which represents 19% of the macrolichen species richness of Fundy National Park on the mainland coast of New Brunswick. Cyanolichens were not found on Kent Island. Nearly 75% of Kent Island's macrolichen species had boreal biogeographical affinities, despite the island's temperate latitude (44°35′N) and low elevation, due to the chilling influence of the locally upwelling Labrador Current. Multi-response Permutation Procedures and Indicator Species Analysis demonstrated non-random habitat associations among Kent Island's macrolichen species and moderate but significant differences in lichen communities among five forest types on the island.

The taxonomic pattern of algal association with lichen fungi may be explained by the fungal selection of algae that are available in the habitat, genetic compatibility between symbionts or mode of reproduction of the lichen. This study examined algal selection among species in the genera Evernia, Pseudevernia and Imshaugia of the Parmeliaceae using nucleotide sequences of the algal Internal Transcribed Spacer (ITS) of the nuclear ribosomal DNA (rDNA), the algal actin gene, the 1512 group I intron and secondary RNA structures. The hypothesis of high selectivity within one species of Evernia examined, E. mesomorpha, was supported suggesting that E. mesomorpha exhibits high selectivity toward its photobiont, which is not shared with other species of lichenized fungi in the same habitat. The eight strongly supported ITS clades correspond with two newly described algal species broadly known as Trebouxia jamesii s.l. and one existing species, T. simplex. The possibility of lateral algal transfer is discussed with reference to algal availability and mode of reproduction of the lichen.

Platyhypnidium pringlei [≡ Eurhynchium pringlei] is an uncommon, montane species of aquatic Brachytheciaceae occurring across central Mexico and in Guatemala. A morphologically distinct form of this moss is found disjunctively in some sheltered coves of the Blue Ridge Mountains in the southeastern United States. Both of these forms are sterile. A similar but more robust female plant is known from Arizona and California. In Himalayan India fertile forms of P. pringlei exist. These are apparently dioicous and have sporophytes with rostrate opercula and weakly roughened setae. Here we describe the sporophytes of P. pringlei for the first time and we discuss the variation, distribution and ecology of the species. Morphologically the several forms of P. pringlei intergrade, but in North America they appear to be geographically isolated.

We tested the monophyly of Platyhypnidium using nuclear ribosomal internal transcribed spacer (ITS) data from 47 collections of Brachytheciaceae. Although most of Platyhypnidium is an artificial segregate of the terrestrial genus Rhynchostegium, P. pringlei has its affinities with Oxyrrhynchium hians [≡ Eurhynchium hians]. Two other closely related aquatic species are E. selaginellifolium from Hawaii and Donrichardsia macroneuron from Texas, and at least one more aquatic relative is known from China. Based on morphological and molecular congruence between these aquatic mosses and terrestrial species of Oxyrrhynchium like O. hians, O. speciosum and O. savatieri, the new combinations O. pringlei, O. selaginellifolium and O. macroneuron are made. Morphologically these aquatic species are characterized by a dark green color, infrequent branching, a loose foliation, a homomallous leaf arrangement, short laminal cells and long costae.

A worldwide revision of Erythrodontium Hampe recognizes seven species. Descriptions, maps and illustrations are given for each species along with a key to the taxa.

Hypogymnia hengduanensis, previously known only from southwestern mainland China, is reported for the first time from Taiwan and Japan. So far it is the only species of Hypogymnia with rimmed holes to be found east of the Hengduan Mountain region of China. Also new to Taiwan are Hypogymnia stricta and H. subarticulata. A key is provided for species of Hypogymnia from Taiwan.

Four new species of Halecania, H. etayoana (saxicolous) and H. fuscopannariae (lichenicolous) both from South America, and H. laevis and H. pannarica, both saxicolous from Europe, are described as new to science. Their ecology, distribution and chemistry are discussed.

Based on extensive new collections, a key to and a list of 11 species of the lichen genus Umbilicaria in Bolivia are provided, and their diversity, altitudinal distribution, biogeographical affinity and reproductive strategies are discussed. Umbilicaria africana, U. aprina, U. cinereorufescens, U. decussata, U. dendrophora, U. leprosa and U. vellea are reported from Bolivia for the first time. The Umbilicaria species of Bolivia belong to several biogeographical elements: an “international” high altitude group of species (4000–5500 m) found in most alpine or Arctic areas of the world (U. aprina, U. cinereorufescens, U. decussata, U. dendrophora, U. nylanderiana, U. vellea), and a central Andean endemic element (U. calvescens, U. leprosa, U. haplocarpa) which completely dominates at lower altitudes (2500–4000 m). In addition the mainly Southern Hemispheric U. africana is abundant in the high alpine areas. A two-phase scenario is suggested where the ancestor of the endemic element colonized and evolved in the Andes while the mountain chain was still fairly low, while the international element is a comparatively recent addition.

Caloplaca chelyae is described as new to science. It is characterized by its scant crustose thallus, spores (12–)13–15 × (7–)8–11 µm, with a narrow equatorial wall-thickening, (1.5–)2–3 µm less than ¼ the length of the spore. This new species, related to subgenus Gyalolechia, was found on bryophytes in the high mountains of the Canary Islands, in El Teide National Park (Tenerife) and La Caldera de Taburiente National Park (La Palma). Possible associated taxa are briefly discussed.

The lignicolous Buellia carballaliana Paz-Bermúdez & Giralt is described as new from Portugal. It is characterized by a thickly crustose to subsquamulose, milk-coffee colored thallus which contains 5-O-methylhiascic acid, and small, unornamented ascospores, belonging to the Buellia-type when mature but showing septal wall thickenings during a brief period of the spore ontogeny ( =  Physconia-type), and always with a well-developed torus.

The foliicolous lichens Aspidothelium hirsutum and Caprettia goderei are described as new from the Godere Forest in southwestern Ethiopia, the former also found in the Kakamega Forest in Kenya.

The two most recent classifications of mosses differ from other systems in the ranking of major lineages typified by Takakia, Sphagnum, Andreaea, Andreaeobryum and peristomate mosses. Here we propose to accommodate all these lineages at the subphylum rather than the informal superclass rank, which requires that the Andreaeophytina stat. nov. and Andreaeobryophytina stat. nov. be erected.

A report of Erpodium hodgkinsoniae from Norfolk Island is based on erroneous determinations of Dicnemon subpiliferum. The Norfolk Island collections of D. subpiliferum are the first report of the species outside of New Caledonia.

A biography of John Walter Thomson (1913–2009), one of the premier lichenologists of his generation, is presented along with a list of his publications.