Meiosis and fertilization represent two fundamental events in the origin, development, and evolution of the eukaryotic life cycle. A life cycle with alternation of generations evolved independently in multiple diverse eukaryote lineages, and variations of this type of life cycle can be found in the photosynthetic red, brown, and green algae and embryophyte land plants. The adaptive advantages of maintaining two multicellular stages necessary for sexual reproduction have been explored on both ecological and genetic levels. However, no hypothesis has been found to be applicable across the diverse lineages. This review summarizes the types of life cycles found in photosynthetic eukaryotes, focusing on those lineages that exhibit an alternation of generations and the adaptive advantages such life cycles may confer. The evolution of the embryophyte lineage and its transition from an aquatic to terrestrial habitat are discussed, as is how the first-diverging embryophyte lineage, the liverworts, display intermediate life cycle characteristics between those of their green algal ancestors and later-evolving embryophytes. In addition, the adaptive advantages of maintaining two multicellular stages are reviewed, particularly the evolution of a multicellular sporophyte through delayed zygotic meiosis and its resulting genetic complexity. The hypothesis developed by Svedelius in 1927 is favored that a lengthened diploid generation with simultaneous increase of the body size allows production of a large number of genetically different gametes via meiosis, which further leads to production of diverse offspring after fertilization.

Bryophytes contain a large number of terpenoids and aromatic compounds. In this article, the chemical constituents of selected liverworts collected in New Zealand, Malaysia, Madagascar, Argentina, Ecuador, and other southern hemispheric countries are discussed. The southern hemisphere is a region of extraordinarily high liverwort diversity. Many of compounds isolated from these liverworts have been represented by novel carbon skeletons and are important chemical markers of a liverwort's genus or family. Many of these compounds also have interesting biological activity.

Ascomycete fungi, identified cytologically from their simple septa and Woronin bodies and genetically diagnosed as belonging to the Rhizoscyphus ericae (D. J. Read) W. Y. Zhuang & Korf (Hymenoscyphus ericae (D. J. Read) Korf & Kernan) aggregate form a range of specialized mutualistic associations with the rhizoids in several families of leafy liverworts. To test the hypothesis that this fungus can produce these associations between liverworts from widely separate geographical regions, we carried out cross-infection experiments between mycobionts that induce branching and septation in the rhizoids in the Schistochilaceae from the southern hemisphere and those from a range of disparate taxa (Bazzania, Calypogeia, Cephalozia, Kurzia, Lepidozia, Odontoschisma) from the northern hemisphere and from Calluna in the Ericaceae. All the fungal isolates produced rhizoid infections identical to those found in nature. The same fungal isolates also invaded the rhizoids of axenically cultured Nardia scalaris, whose stems in nature harbor a basidiomycete and the fungus-free species Jungermannia gracillima, but balanced relationships in these cross infection experiments were not established. Consideration of recent liverwort phylogenies placing the Sch istochilaceae as sister to all the other fungus-containing clades of leafy liverworts, together with dating of this family in the Triassic, suggests that liverwort–ascomycete associations may have pre-dated ericoid mycorrhizas. However, the diverse cytology of these associations and their discontinuous distribution between families in the leafy liverworts indicate more recent and multiple origins including host swapping from the Ericales.

Early stages of leaf development were studied in Schistochila appendiculata (Hook.) Dumort. ex Trevis., S. nobilis (Hook.) Trevis., Pachyschistochila subhyalina (R. M. Schust.) R. M. Schust. & J. J. Engel, and Gottschea conchophylla (E. A. Hodgs. & Allison) Grolle & Zijlstra, using transverse microtome sections. Like other groups of leafy liverworts, all four species have apical cells with three cutting faces and two primary leaf initials from which bilobed leaves are initiated. Apical cell geometry and early patterns of merophyte development are the same for all taxa studied, including those without underleaves. The wing of the leaf develops very early, shortly after the leaf lobes begin to form. The initial sign of wing development is the outward expansion and protrusion of a row of cells along the keel and the basiscopic or posterior margin of the ventral lobe. These cells undergo subsequent divisions so that transverse sections of the young leaves appear Y-shaped.

Karyological observations were made on 14 species of liverworts from China and Singapore. The chromosome numbers of four species, Metzgeria consanguinea Schiffn. (n=8), Riccardia elata (Steph.) Schiffn. (n=9 m), Riccardia graeffei (Steph.) Hewson (n=9 m), and Riccardia kodamae Mizut. & S.Hatt. (n=9 m), are reported for the first time. The karyotype formulae of Riccardia elata, Metacalypogeia cordifolia (Steph.) Inoue (n=9), Pallavicinia lyellii (Hook.) Carruth. (n=8), Pellia epiphylla (L.) Corda (n=8 m), and Scapania ciliata Sande Lac. (n=8 m) are provided. Two different chromosome numbers (n=9, n=9 m) were found in Jubula javanica Steph. Of 14 species investigated cytologically, eight species have an m-chromosome. Riccardia elata is new to the liverwort flora of China.

Liverworts (Marchantiophyta) form a conspicuous and important component in many terrestrial ecosystems throughout the world. Despite of their significance and abundance, studies of various aspects on global plant species richness and distribution patterns have almost exclusively focused on vascular plants. Yet, comprehensive studies of liverwort plant diversity have many implications and broad applications. We use a preliminary dataset that unites liverwort nomenclature, taxonomy, and geography based on some 60,000 records. Global maps are produced for the taxonomic ranks of species, genus, and family to provide a rapid guide of diversity across political units worldwide. The usefulness of higher level taxon analyses was investigated at the genus and family level to test the relationship with species richness. A reduced set of taxonomic ranks other than species has been proved to be useful for rapid and cost-effective assessment of biodiversity. We provide the first examination of how well this method performs for liverworts. Generic richness was slightly more accurately related to species richness than that of families, indicating surrogacy at this taxonomic level as a promising approach for the prediction of liverwort species richness. Finally, given the fact that vascular plant diversity and distribution patterns are often given high consideration in evaluating global networks of protected areas and biodiversity hotspots, we present a comparison of centers of species richness between liverworts and vascular plants. Several regions of high liverwort species richness lie outside the highest centers of vascular plant species richness. We conclude with ideas for future studies of the dataset, which has many exciting implications and applications for the study of liverwort distribution and diversity patterns.

The significance and importance of checklists is briefly discussed. A comprehensive current checklist of liverwort checklists is provided with the starting date of 1900. In order to increase the value of this list, the checklists have been categorized according to whether the publications are specimen-based, record original citations, or list the extent of the territory covered. Although there are checklists for many territories throughout the world, there remain, alarmingly, substantial portions of the globe that either lack checklists entirely or have checklists that are woefully out of date.

The genus Hamatostrepta and its single new species H. concinna are described from the Sino-Burmese border region of Asia. The genus is related to Anastrepta but differs in its strongly deflexed, deeply trilobed leaves. Ecologically the species grows in alpine liverwort/dwarf shrub heath associated with dwarf Rhododendrons.

The genus Phaeolejeunea is new to the Fiji Islands, represented by one species previously known only from 'Eua (Tonga Islands) under the name Phaeolejeunea etesseana Mizut. ssp. amicorum Hürl. As a result of a study of all species of the genus, this taxon proved sufficiently distinct as to warrant recognition at the rank of species. It is endemic to the Fiji and Tonga islands, at the border of Eastern Melanesia and Western Polynesia in the Southern Pacific. First observations on the oil-bodies of Phaeolejeunea are given.

The genus Frullania was previously known to be represented in the Fiji Islands by 20 species. From recent collections, 17 species were identified, of which five species proved to be new to the islands: Frullania angulistipa, Frullania baladina, Frullania chevalieri, Frullania ericoides, and Frullania gracilis. One other, Frullania vivipara, is described as new to science. The enumeration is followed by a phytogeographic evaluation.

We recognize three species of Mnioloma for Australasia. Mnioloma novaezelandiae J.J.Engel is known only from New Zealand. The plants upon which the Australian record of M. novaezelandiae was based are referred to Mnioloma cf. fuscum (Lehm.) R. M. Schust., for, while similar to this species, we have been unable to substantiate their placement either within this species or as a separate entity. We describe Mnioloma stamatotonum as new for plants with crenulate leaf margins, ovate leaves, and underleaves with irregular margins. This plant is known from two specimens, one from Mt. Lewis (Queensland, Australia), the other from Mt. Kouakoué (New Caledonia). Mnioloma novaezelandiae appears to display considerable clinal variation, the quantification of which would inform the grouping decisions we make here.

A new species, Bazzania engelii, is described from two sites on Stockton Plateau, a sloping plateau between 200 and 1100 m asl northeast of Westport, South Island, New Zealand. Bazzania engelii is compared with other New Zealand Bazzania species but is not placed in a subgenus. The species has a superficial similarity to B. nitida, but the frequent production of ventral-intercalary branches with normal leaves suggests a relationship with B. exempta.

An illustrated key to the currently accepted 10 species of Porella in North America north of Mexico is presented. The only known American locality of P. gracillima is described.

The liverwort Odontoschisma engelii Gradst. & Burghardt sp. nov. (Cephaloziaceae) is described from páramo vegetation of southern Ecuador and Venezuela. The new species is a member of Odontoschisma section Denudatae R. M. Schust. and differs from all known species of the genus by the strongly elongated leaves.

Taxonomic revision of the liverwort genus Tylimanthus Mitt. (Acrobolbaceae) in tropical America, Africa, and Macaronesia leads to the recognition of one widespread and variable species, T. laxus (Lehm. & Lindenb.) Spruce. Tylimanthus approximatus (Lindenb.) Besch., T. azoricus Grolle & Perss., T. fendleri (Gottsche) Steph., T. herzogii Steph., T. madeirensis Grolle & Perss., T. ruwenzorensis S. W. Arnell, T. setaceo-ciliatus Steph., T. striolatus Steph., and T. subtilis Steph. are new synonyms of T. laxus, and T. bispinosus J. B. Jack & Steph. and T. cuneifolius Steph. are excluded from Tylimanthus. Lectotypes are proposed for T. approximatus, T. herzogii, and T. laxus.

The bryophyte flora of the Pacific Northwest includes three previously known species of tuber-producing hornworts that occupy seasonally dry habitats. Except for Phymatoceros bulbiculosus (Brot.) Stotler, W.T. Doyle & Crand.-Stotl., which was recently segregated from Phaeoceros Prosk. on the basis of a combination of morphological and molecular studies, no comprehensive studies of these taxa have been undertaken since their naming. As a consequence, confusion exists regarding their taxonomic identity. This study combines field observations with morphological and molecular data to evaluate the systematic status of Phaeoceros hallii (Austin) Prosk. and Phaeoceros pearsonii (M. Howe) Prosk. These data support the recognition of a new species, Phaeoceros proskaueri Stotler, Crand.-Stotl. & W. T. Doyle, in this complex of related taxa. In addition, morphological studies of the lectotype of Anthoceros tuberosus Taylor (= Phaeoceros tuberosus (Taylor) Prosk.), which is formally designated here, and the holotype of Paraphymatoceros diadematus Hässel demonstrate that neither is related to P. hallii, P. pearsonii or P. proskaueri. Phaeoceros tuberosus is aligned with P. laevis (L.) Prosk. and Paraphymatoceros hallii (Austin) Hässel is placed as a synonym of Phaeoceros hallii. Paraphymatoceros diadematus is postulated to be congeneric with Phaeomegaceros Duff et al., and the following new combinations are made: Paraphymatoceros fimbriatus (Gottsche) Stotler, Paraphymatoceros coriaceus (Steph.) Stotler, Paraphymatoceros hirticalyx (Steph.) Stotler, and Paraphymatoceros skottsbergii (Steph.) Stotler.

Four species within the hornwort genus Phaeoceros are recognized and described for Australia: the cosmopolitan P. carolinianus (Michx.) Prosk.; two new combinations of taxa endemic to Australia—P. evanidus (Steph.) Cargill & Fuhrer comb. nov., P. inflatus (Steph.) Cargill & Fuhrer comb. nov.; and a species new to science, P. engelii Cargill & Fuhrer sp. nov. A key to all four species is also given.

The known and presumed origins and meanings of the accepted names of liverwort and hornwort genera known from Australia are outlined.