A working checklist of accepted taxa worldwide is vital in achieving the goal of developing an online flora of all known plants by 2020 as part of the Global Strategy for Plant Conservation. We here present the first-ever worldwide checklist for liverworts (Marchantiophyta) and hornworts (Anthocerotophyta) that includes 7486 species in 398 genera representing 92 families from the two phyla. The checklist has far reaching implications and applications, including providing a valuable tool for taxonomists and systematists, analyzing phytogeographic and diversity patterns, aiding in the assessment of floristic and taxonomic knowledge, and identifying geographical gaps in our understanding of the global liverwort and hornwort flora. The checklist is derived from a working data set centralizing nomenclature, taxonomy and geography on a global scale. Prior to this effort a lack of centralization has been a major impediment for the study and analysis of species richness, conservation and systematic research at both regional and global scales. The success of this checklist, initiated in 2008, has been underpinned by its community approach involving taxonomic specialists working towards a consensus on taxonomy, nomenclature and distribution.

Phylogenetic relationships and character evolution in the core Ptychanthoideae (Lejeuneaceae, Marchantiophyta), with a focus on Thysananthus, are assessed based on molecular (plastid psbA–trnH, trnG, trnL–F, trnS–rps4, nrITS), morphological–anatomical, and phytochemical data. Generic relationships are molecularly well–resolved and confirm the placement of Mastigolejeunea pancheri and the monotypic Dendrolejeunea fruticosa in Thysananthus. Most morphological characters currently used to distinguish genera in Ptychanthoideae are homoplastic according to ancestral state reconstruction. Molecular and phytochemical data suggest the occurrence of polyphyletic species in Thysananthus and Mastigolejeunea. Careful study of the polyphyletic taxa revealed morphological differences between some of the intraspecific clades, which correlated with synonymized or novel species. Incongruence between plastid and ITS data in M. pancheri indicated the occurrence of a putative hybrid, the first one recorded in Lejeuneaceae and the first in liverworts inferred from phylogenetic data.

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Mastigolejeunea is morphologically close to Thysananthus and the separation of these two genera has long been controversial. The relationship between Mastigolejeunea and Thysananthus is assessed based on Bayesian inference and maximum likelihood analyses of plastid psbA-trnH, trnG and trnL-F, and nuclear ITS. Mastigolejeunea was resolved as sister to Thysananthus with moderate support, but M. calcarata was nested in Thysananthus subsect. Anguiformes and M. florea was resolved in Spruceanthus. Because diagnostic morphological features separating Mastigolejeunea from Thysananthus are lacking, Mastigolejeunea is treated as a subgenus of Thysananthus. The latter group becomes the second largest genus of Lejeuneaceae subfam. Ptychanthoideae with 30 species, and is one of the largest genera of liverworts that has been monographed worldwide.

The number of available liverwort fossils substantially increased within the past decade, which is mainly due to new findings from Cretaceous and Cenozoic amber deposits. Many of them, however, are fragmentary and not predestined for consideration in evolutionary analyses. Here, we list those liverwort fossils that we suggest as suitable for calibrating phylogenetic reconstructions, along with brief descriptions, justification of their use, and age information. Our recommendations are based on thorough microscopic investigation of available fossils from worldwide amber collections including recent findings. We recommend that the following 42 fossil taxa can be used as confident minimum age constraints in phylogenetic reconstructions: Acrolejeunea ucrainica (35 Ma), Anastrophyllum rovnoi (35 Ma), Bazzania polyodus (34 Ma), Blepharolejeunea obovata (15 Ma), the genus Bryopteris with B. bispinosa and B. succinea (15 Ma), Calypogeia stenzeliana (34 Ma), Cephaloziella nadezhdae (35 Ma), the genus Ceratolejeunea with C. antiqua, C. palaeomexicana, and C. sublaetefusca (15 Ma), Cheilolejeunea latiloba (34 Ma), Cheirorhiza brittae (158 Ma), Cololejeunea sp. (15 Ma), Cyclolejeunea archaica (15 Ma), Dibrachiella grollei (15 Ma), Diettertia montanensis (112 Ma), Drepanolejeunea eogena (15 Ma), the genus Frullania with F. baerlocheri, F. cretacea, and F. partita (99 Ma), Frullania subgen. Frullania with F. casparyi (34 Ma) and F. riclefgrollei (35 Ma), F. subgen. Trachycolea with F. rovnoi (35 Ma) and F. schumannii (34 Ma), Gackstroemia cretacea (99 Ma), Geocalyx heinrichsii (34 Ma), the genus Lejeunea with L. hamatiloba, L. miocenica, L. resinata, and L. urbanioides (15 Ma), Lopholejeunea subnigricans (15 Ma), Marchantites cyathodoides (228 Ma), Marchesinia brachiata (15 Ma), Metzgeriothallus sharonae (383 Ma), Microlejeunea nyiahae (52 Ma), Neurolejeunea macrostipula (15 Ma), Nipponolejeunea europaea (34 Ma), Notoscyphus balticus (34 Ma), Odontoschisma (sect. Iwatsukia) dimorpha (34 Ma), Plagiochila groehnii (34 Ma), Porella subgrandiloba (34 Ma), Protolophozia kutscheri (34 Ma), Radula (subgen. Odontoradula) cretacea (99 Ma), R. (subgen. Amentuloradula) heinrichsii (99 Ma), Scapania hoffeinsiana (34 Ma), Solenostoma berendtii (34 Ma), Spruceanthus polonicus (34 Ma), Stictolejeunea squamata (15 Ma), Tetralophozia groehnii (34 Ma), Thysananthus auriculatus (15 Ma), Thysananthus contortus (34 Ma). Furthermore, we transfer Lophozia kutscheri to Protolophozia, Archilejeunea grollei to Dibrachiella, Frullania ucrainica to Acrolejeunea, and Mastigolejeunea extincta to Spruceanthus, based on new fossil evidence and morphological revisions.