Asterella is a large group of chambered liverworts with a worldwide distribution; the genus is primarily defined by the presence of a pseudoperianth, a cage-like structure surrounding each capsule in the carpocephalum. Molecular phylogenies of a range of Asterella species were reconstructed using two chloroplast DNA sequences (ca. 70% of the matK coding region and the trnL intron), in order to study relationships of species within the genus and to test hypothetical relationships predicted by spore ornamentation types. The matK gene has not been used previously in bryophytes. Sixteen species of Asterella were sampled; representatives of the other four (smaller) genera of Aytoniaceae were also sampled i.e., Cryptomitrium (one species), Mannia (two species), Reboulia (one species), and Plagiochasma (two species). Outgroups selected from other families of Marchantiopsida were Athalamia (Cleveaceae), Lunularia (Lunulariaceae), Marchantia (Marchantiaceae), Riccia (Ricciaceae), and Targionia (Targioniaceae). Three analyses were performed: 1) matK, 2) trnL, and 3) a combined weighted matK/trnL analysis. The last analysis produced a single most parsimonious tree. Analyses rooted on Lunularia produced a stable resolved tree topology, with very strong support for Aytoniaceae as a monophyletic group, but with Asterella appearing as a paraphyletic genus including its four sister-genera. Paraphyly of ‘Asterella’ suggests that the pseudoperianth is actually a plesiomorphy within the family that has been lost during at least three separate evolutionary events. The major clades within Aytoniaceae have distinctive spore ornamentation types, and some of the infrageneric groups of Asterella inferred from spore characters are supported by the molecular analyses. The traditional subfamily groupings of genera within Aytoniaceae, however, are not supported. The taxonomic implications of the study are discussed.

The green algal symbionts of the lichenized fungus Letharia are identified as members of the morphospecies Trebouxia jamesii, based on ITS sequences that place them in a molecularly diverse clade with other lichen algae also identified as T. jamesii. However, based on additional sequence from a second locus, actin, T. jamesii is seen to consist of many phylogenetic species. A clade of six to seven closely related phylogenetic species of T. jamesii are symbiotic with five of the six phylogenetic species of Letharia. Within this broad level of specificity, there are also narrower patterns of specificity. For example, three cryptic species of T. jamesii were found only in two species of Letharia in California, a pattern that may be due either to biogeography, or to Letharia phylogenetically tracking Trebouxia. Allopatric Letharia vulpina has switched to a genetically distant phylogenetic species within the T. jamesii morphospecies, suggesting that habitat plays a role in specificity. One phylogenetic species of T. jamesii was found to have a recombining population structure, as two alleles of two loci were found in all four pairwise combinations among the haploid genotypes of that species. This result suggests that Trebouxia, a genus in which sexual structures have never been observed, is nevertheless recombining.

In 1995, we installed surface-sterilized, rough-barked and smooth-barked tree branches in clearcuts, young forests, and old growth. Half of the experimental branches were inoculated with propagules of the epiphytic cyanolichen, Lobaria oregana. In 1997, we concluded that L. oregana was associated with old-growth Douglas-fir forests because of dispersal limitation; addition of L. oregana propagules resulted in a marked increase in establishment rates. In 1999, we revisited the experiment to determine whether other epiphytes had colonized the tree branches. We also checked to see if the 1997 results of the experiment persisted. A total of 26 epiphyte genera (nine bryophytes and 17 lichens) had colonized the branches. Lichen colonization was generally fastest in clearcuts. Colonization by alectorioid lichens was rapid in both clearcuts and old growth but slow in young forests. In contrast, bryophyte colonization was relatively rapid in all age classes. Epiphyte colonization was generally more rapid on smooth bark than on rough bark, although Cladonia was more frequent on rough-barked branches. Bryophytes, cyanolichens, and Sphaerophorus globosus were more frequent on inoculated branches than on control branches, implying that the L. oregana propagule mixture used in 1995 was contaminated with other epiphytes. Like L. oregana, these species may also be dispersal-limited. The number of established L. oregana thalli in clearcuts and young stands decreased from 1997 to 1999, but the number of thalli remained relatively stable in old growth. After four years, established L. oregana thalli were larger in clearcuts than in either young stands or old growth. Overall, the fourth-year results of our experiment confirm the importance of dispersal limitation as the cause of old-growth association in L. oregana in western Oregon.

The Panariaceae sensu lato of North America are shown to contain 51 species in ten genera: Degelia (1), Erioderma (3), Fuscopannaria (25), Leioderma (1), Moelleropsis (1), Pannaria (8), Parmeliella (5), Protopannaria (1), Psoroma (3), and Santessoniella (3). The following new taxa are described: Fuscopannaria alaskana, F. aurita, F. coralloidea, F. crustacea, F. hookerioides, F. leprosa, F. pacifica, F. ramulina, F. thiersii, Pannaria lurida ssp. quercicola, P. subfusca, and Parmeliella appalachensis. The following new combinations proved necessary: Fuscopannaria californica (Tuck.), F. cheiroloba (Müll. Arg.), F. incisa (Müll. Arg.), Pannaria lurida ssp. russellii (Tuck.), Parmeliella stylophora (Vain.), Protopannaria (Gyeln.), Protopannaria pezizoides (G. H. Weber), and Santessoniella crossophylla (Nyl.). All names are typified and keys are provided to all taxa. The genus Fuscopannaria has an evolutionary center on the Pacific coast where it appears to have evolved taxa for most available niches from coastal rocks (F. maritima) to high mountain peaks (F. hookerioides), and from cool damp habitats (F. alaskana) to warm, dry ones (F. californica). Several species in the eastern parts, like F. leucosticta and F. sorediata, reappear in Japan and are additions to the Tertiary relic element of the North American flora. The importance of recognizing ecogeographic elements is pointed out.

Three taxa of pyrenocarpous lichens from the Sonoran Region are described as new: Placidium lacinulatum var. erythrostratum is characterized by a reddish medullary layer and broadly ellipsoidal ascospores. It is known from Arizona, California, and Mexico. Placopyrenium insuetum from Mexico is recognized by its rosulate, brown, epruinose thallus. Verrucaria rubrocincta, yet known only from Arizona and Mexico, is characterized by an endolithic thallus and a reddish pigmented, dimidiate involucrellum.

The bark of isolated Oregon white oaks (Quercus garryana Dougl.) supports a distinctive bryophyte flora. Savannah oaks are now rare, but isolated oaks remain in urban and agricultural areas. I documented the bryophyte flora and searched for Syntrichia laevipila var meridionalis, previously considered rare in the Pacific Northwest, on isolated oaks in urban and agricultural areas throughout the Willamette Valley. Most bryophytes on the wet sides of trunks were pleurocarpous mat-formers, while most on the dry sides were acrocarpous cushion- or turf-formers. Isolated oaks and their distinctive bryophyte community occurred to 201 m elevation, but S. laevipila var meridionalis was present only at or below 100 m elevation, never without the variety laevipila. Dry bark bryophytes were often heavily grazed, possibly by springtails or slugs. Gemmipary, present among several oak-dwelling species, may be a response to grazing or exhaust fumes.

Many studies have shown that certain species of bryophytes and lichens require old-growth forests for their survival. The objective of this study is to evaluate the composition and diversity of epiphytic lichen and bryophyte communities on trembling aspen (Populus tremuloides), as a function of the time elapsed since stand initiation. The study was carried out in the forests surrounding Lake Duparquet, in the southwestern part of Québec's boreal forest. Stands representing different post-fire successional stages, corresponding to 278, 125, 79, and 51 yr since the last fire were selected. For each stand age, 10 trees from four different sites were sampled. A total of 75 species of non-vascular plants were found, including 34 species of mosses, seven species of liverworts, and 34 species of lichens. More species were observed in the 278-yr old stand, which also contained a greater number of exclusive species. In a correspondence analysis performed on species presence/absence data, axes one and two were correlated with distance from the closest unburnt area and time since fire. For each tree, species richness, diversity, and cover indices were calculated and compared for the different stand ages. These indices tended to be higher in the 79-yr old stand and lower in the 51-yr old stand. By using mixed log-linear models, we found that the frequency of occurrence of some species was linked to the time since fire, and others species to tree age. Old-growth forests are important to bryophytes and lichens since they have a greater number of species and some species are found exclusively or more frequently in old-growth forests. Furthermore, each stand age has some species associated with it. Therefore, forest management practices should be adopted to maintain all successional stages present in the natural forest landscape in order to preserve the diversity of non-vascular plants.

Sphaerotheciella koponenii P. Rao, sp. nov. is described from Hunan Province, China. It appears closely related to the American S. pinnata (B.S.G.) Manuel, but has different costae in the perichaetial leaves, different capsule shape and exostome ornamentation, and entire to crenate apices of the stem leaves. The new species is illustrated and a key to all species of the genus is presented.

The bryophyte communities on glacial erratic boulders in the Adirondack Mountains of New York are used as an experimental system to test the predictions of island biogeographic theory. Moss species composition, abundance, richness, and diversity were determined for 39 boulders. Bryophyte species richness on these insular habitats ranges from 3 to 14. Competitive dominance of the component moss species was determined. Boulders were characterized as to size, degree of isolation, and microhabitat heterogeneity. Patterns of disturbance and gap formation in the moss cover, and patterns of recolonization were quantified. The distribution of bryophyte species among individual boulders does not conform to the predictions of island biogeographic theory. Neither the size of the boulder nor its degree of isolation are significantly related to species richness. Richness was also found to be independent of the abundance of the competitive dominants. Overall measures of microhabitat heterogeneity were not correlated with species richness, although a weak relationship with microtopographic diversity was detected. We suggest that the high frequency of gap formation on these boulders maintains the community in a non-equilibrium state. The observed patterns of species richness may be the result of population level processes that govern dispersal and establishment among boulders and among gaps on the boulder surface.

Metzgeria angusta Steph., a species recorded from numerous localities in the New World, is lectotypified and redescribed. The syntype material is heterogeneous and includes seven different species. As lectotypified here, Metzgeria angusta is similar to M. albinea Spruce and is reduced to varietal status under the latter, as Metzgeria albinea var angusta (Steph.) Costa & Gradst. stat. nov. (= Metzgeria angusta var pectinata Schiffn., syn. nov.). The variety occurs in Mexico, Trinidad, and southeastern Brazil.

Grimmia herzogii Broth., synonyms G. nigella Herzog, and G. trollii Herzog, is described, and contrasted with G. longirostris Hook. Although these two names have been considered by some as synonyms, they are here recognized as distinct species.

Grimmia mexicana Greven is characterized by obtuse to rounded or subcucullate leaf apices and by the outer plates of the peristome teeth that are smooth and hyaline or transluscent. These and other morphological differences distinguish it from G. ochyriana Muñoz that is thus excluded from the neotropical moss flora.

Culbersonia americana, a new foliose lichen genus and species, is described from the mountains of Arizona and Peru. Although it has a unique set of identifying characters and apparently belongs to the family Physciaceae, all the material seen so far lacks apothecia, and evidence for familial placement for now remains inconclusive.

As a result of a project using two chloroplast loci, the trnL-trnF region and the rps4 gene, to test the monophyly of pleurocarpous mosses as a group and the traditional three orders contained in it, several novel generic alliances were revealed. Of particular interest are the inclusion of the Ptychomniaceae and Garovagliaceae in the Hookeriales, as well as generic inclusions in the Anomodontaceae, Brachytheciaceae, Amblystegiaceae sensu lato, and Sematophyllaceae.

Lecanora thysanophora R. C. Harris, n. sp. is described. It is a common lichen in eastern North America, most often found as a sterile corticolous crust, but apothecia are not uncommon when the species grows along streams. Besides being recognizable in the field, it is distinctive chemically, containing usnic acid, zeorin, often porphyrilic acid, and several species-specific terpenoids.

Three small populations of the rare allopolyploid peat moss species Sphagnum troendelagicum are studied using RAPD markers. Contrary to expectations, levels of neutral genotypic and haplotypic variation are moderately high in this seemingly asexual species. A model is presented for estimating relative impact of recombination on genetic variability. Recombinations appear to occur rarely in studied populations compared to mutation events, even though little significant linkage disequilibrium exists. We hypothesize that multiple origins of the species due to recurrent hybridization events may partially account for the observed variability.

Harpidium nashii Scheidegger, sp. nov. is described as new to science. The species is similar to Harpidium rutilans, hitherto the only species of the genus, but differs considerably in thallus morphology. Harpidium nashii is known from four localities in Baja California and California. This is the first report of the genus Harpidium from outside Europe.