Sanna Huttunen

ORIGIN AND EVOLUTION OF THE NORTHERN HEMISPHERE DISJUNCTION IN THE MOSS GENUS HOMALOTHECIUM (BRACHYTHECIACEAE)

Competing hypotheses that rely either on a stepping-stone dispersal via the North Atlantic or the Bering land bridges, or more recent transoceanic dispersal, have been proposed to explain the disjunct distribution of Mediterranean flora in southern Europe and western North America. These hypotheses were tested with molecular dating using a phylogeny of the moss genus Homalothecium based on ITS, atpB-rbcL, and rpl16 sequence data. The monophyly of two main lineages in Western Palearctic (Europe, central Asia and north Africa) and North America is consistent with the ancient vicariance hypothesis. The monophyly of Madeiran H. sericeum accessions supports the recognition of the Macaronesian endemic H. mandonii. A range of absolute rates of molecular evolution documented in land plants was used as probabilistic calibration prior by a Bayesian inference implementing a relaxed-clock model to derive ages for the nodes of interest. Our age estimates for the divergence of the American and Western Palearctic Homalothecium clade (5.7 Ma, IC 3.52-8.26) and the origin of H. mandonii (2.52 Myr IC 0.86-8.25) are not compatible with the ancient vicariance hypothesis. Age estimates suggests that species distributions result from rare instances of dispersal and subsequent sympatric diversification. The calibrated phylogeny indicates that Homalothecium has undergone a fast radiation during the last 4 Myr, which is consistent with the low levels of morphological divergence among sibling species.

On resurrection of the families Pseudoleskeaceae Schimp. and Pylaisiaceae Schimp. (Musci, Hypnales)

Results from our analysis of chloroplast trnL-trnF and nuclear ITS1 and ITS2 sequence data and 35 morphological characters for 134 taxa of pleurocarpous mosses provide an evidence for resurrecting two moss families, Pseudoleskeaceae and Pylaisiaceae. Both these families were described by Schimper in 1860, but soon afterwards included in Leskeaceae and Hypnaceae, respectively, and apparently never used in the 20 t h century. However, sequence-level data analysis (chloroplast encoded trnL intron and trnL-trnF spacer, nuclear encoded ITS1 & ITS2), and combined molecular and morphological analysis demonstrate the remote position of (1) the Lescuraea-group from the main part of Leskeaceae; and (2) a group of species belonging to Pylaisia, Homomallium and Hypnum (sections others than sect. Hypnum} from Hypnum sect. Hypnum (with H. cupressiforme as the type of the genus).

Phylogenetic analyses reveal high levels of polyphyly among pleurocarpous lineages as well as novel clades

Abstract Phylogenetic analyses of the Hypnales usually show the same picture of poorly resolved trees with a large number of polyphyletic taxa and low support for the few reconstructed clades. One odd clade, however, consisting of three genera that are currently treated either within the Leskeaceae (Miyabea) or Neckeraceae (Homaliadelphus and Bissetia), was retrieved in a previously published phylogeny based on chloroplast rbcL. In order to elucidate the reliability of the observed Homaliadelphus - Miyabea - Bissetia -clade (HMB-clade) and to reveal its phylogenetic relationships a molecular study based on a representative set of hypnalean taxa was performed. Sequence data from all three genomes, namely the ITS1 and 2 (nuclear), the trnS-rps4-trnT-trnL-trnF cluster (plastid), the nad5 intron (mitochondrial), were analyzed. Although the phylogenetic reconstruction of the combined data set was not fully resolved regarding the backbone it clearly indicated the polyphyletic nature of various hypnalean families, such as the Leskeaceae, Hypnaceae, Hylocomiaceae, Neckeraceae, Leptodontaceae and Anomodontaceae with respect to the included taxa. In addition the results favor the inclusion of the Leptodontaceae and Thamnobryaceae in the Neckeraceae. The maximally supported HMB-clade consisting of the three genera Homaliadelphus (2–3 species), Miyabea (3 species) and Bissetia (1 species) is resolved sister to a so far unnamed clade comprising Taxiphyllum aomoriense, Glossadelphus ogatae and Leptopterigynandrum. The well-resolved and supported HMB-clade, here formally described as the Miyabeaceae, fam. nov. is additionally supported by morphological characters such as strongly incrassate, porose leaf cells, a relatively weak and diffuse costa and the presence of dwarf males. The latter are absent in the Neckeraceae and the Leskeaceae. It is essentially an East Asian family, with one species occurring in North America.

Evolution of the Neckeraceae (Bryophyta): Resolving the backbone phylogeny

Abstract Earlier phylogenetic studies, including species belonging to the Neckeraceae, have indicated that this pleurocarpous moss family shares a strongly supported sister group relationship with the Lembophyllaceae, but the family delimitation of the former needs adjustment. To test the monophyly of the Neckeraceae, as well as to redefine the family circumscription and to pinpoint its phylogenetic position in a larger context, a phylogenetic study based on molecular data was carried out. Sequence data were compiled, combining data from all three genomes: nuclear ITS1 and 2, plastid trnS‐rps4‐trnT‐trnL‐trnF and rpl16, and mitochondrial nad5 intron. The Neckeraceae have sometimes been divided into the two families, Neckeraceae and Thamnobryaceae, a division rejected here. Both parsimony and Bayesian analyses of molecular data revealed that the family concept of the Neckeraceae needs several further adjustments, such as the exclusion of some individual species and smaller genera as well as the inclusion of the Leptodontaceae. Within the family three well‐supported clades (A, B and C) can be distinguished. Members of clade A are mainly non‐Asiatic and nontropical. Most species have a weak costa and immersed capsules with reduced peristomes (mainly Neckera spp. ) and the teeth at the leaf margins are usually unicellular. Clade B members are also mainly non‐Asiatic. They are typically fairly robust, distinctly stipitate, having a single, at least relatively strong costa, long setae (capsules exserted), and the peristomes are well developed or only somewhat reduced. Members of clade C are essentially Asiatic and tropical. The species of this clade usually have a strong costa and a long seta, the seta often being mammillose in its upper part. The peristome types in this clade are mixed, since both reduced and unreduced types are found. Several neckeraceous genera that were recognised on a morphological basis are polyphyletic (e.g. Neckera, Homalia, Thamnobryum, Porotrichum). Ancestral state reconstructions revealed that currently used diagnostic traits, such as the leaf asymmetry and costa strength are highly homoplastic. Similarly, the reconstructions revealed that the ‘reduced’ sporophyte features have evolved independently in each of the three clades.

And if Engler was Not Completely Wrong? Evidence for Multiple Evolutionary Origins in the Moss Flora of Macaronesia

The Macaronesian endemic flora has traditionally been interpreted as a relict of a subtropical element that spanned across Europe in the Tertiary. This hypothesis is revisited in the moss subfamily Helicodontioideae based on molecular divergence estimates derived from two independent calibration techniques either employing fossil evidence or using an Monte Carlo Markov Chain (MCMC) to sample absolute rates of nucleotide substitution from a prior distribution encompassing a wide range of rates documented across land plants. Both analyses suggest that the monotypic Madeiran endemic genus Hedenasiastrum diverged of other Helicodontioideae about 40 million years, that is, well before Macaronesian archipelagos actually emerged, in agreement with the relict hypothesis. Hedenasiastrum is characterized by a plesiomorphic morphology, which is suggestive of a complete morphological stasis over 40 million years. Macaronesian endemic Rhynchostegiella species, whose polyphyletic origin involves multiple colonization events, evolved much more recently, and yet accumulated many more morphological novelties than H. percurrens. The Macaronesian moss flora thus appears as a complex mix of ancient relicts and more recently dispersed, fast-evolving taxa.

Disentangling knots of rapid evolution: origin and diversification of the moss order Hypnales

Abstract The Hypnales are the largest order of mosses comprising approximately 4200 species. Phylogenetic reconstruction within the group has proven to be difficult due to rapid radiation at an early stage of evolution and, consequently, relationships among clades have remained poorly resolved. We compiled data from four sequence regions, namely, nuclear ITS1–5·8S–ITS2, plastid trnL–F and rps4, and mitochondrial nad5, for 122 hypnalean species and 34 species from closely related groups. Tree topologies from both Bayesian and parsimony analyses resolve the order as monophyletic. Although inferences were made from fast-evolving genes, and despite strong phylogenetic signal in the nuclear ITS1–5·8S–ITS2 data, monophyly, as well as backbone nodes within the Hypnales, remains rather poorly supported except under Bayesian inferences. Ancestral distribution based on Bayesian dispersal-vicariance analysis supports a Gondwanan origin of the Hypnales and subsequent geographical radiation in the area of the former Laurasian supercontinent. Reconstruction of historical biogeography is congruent with mainly tropical and Gondwanan distributions in the sister groups Hypnodendrales, Ptychomniales, and Hookeriales, and with the dating for the oldest pleurocarp and hypnalean fossils. We contrast groupings in the phylogenetic tree with recent classifications and other phylogenetic inferences based on molecular data, and summarise current knowledge on the evolutionary history of, and relationships among, the Hypnales.

Back to the Future? Molecules Take Us Back to the 1925 Classification of the Lembophyllaceae (Bryopsida)

Abstract Although the Lembophyllaceae has undergone considerable revision during the last century, the generic and familial level relationships of this pleurocarpous moss family are still poorly understood. To address this problem, a generic revision of the Lembophyllaceae based on molecular data was undertaken. We analyzed two plastid markers, the trnL-trnF and the psbT-psbH region in combination with the ITS2 of nuclear ribosomal DNA. The molecular data reveal that the current circumscription of the family is too narrow and that several genera previously placed in the Lembophyllaceae should be reincluded. The family includes: Bestia, Camptochaete, Dolichomitra, Dolichomitriopsis, Fallaciella, Fifea, Isothecium, Lembophyllum, Looseria stat. nov., Pilotrichella, Rigodium, Tripterocladium, and Weymouthia. Looseria contains a single species: Looseria orbiculata comb. nov. Acrocladium is excluded and provisionally accommodated in the Lepyrodontaceae. Generic limits supported by the molecular data support a return to the early twentieth century family concept of Brotherus. The analyses indicate that the segregate genus Orthostichella is distinct from its parent genus Pilotrichella, probably at the family level. Whereas Pilotrichella is resolved within the Lembophyllaceae, Orthostichella clusters with Porotrichum and Porothamnium forming a clade (OPP-clade) sister to the remaining Neckeraceae and Lembophyllaceae. Hence, the Neckeraceae is paraphyletic. Recognition of the OPP-clade as a new family is desirable but awaits the results of detailed ongoing morphological studies.

Morphology informed by phylogeny reveals unexpected patterns of species differentiation in the aquatic moss Rhynchostegium riparioides s.l.

Bryophyte floras typically exhibit extremely low levels of endemism. The interpretation, that this might reflect taxonomic shortcomings, is tested here for the Macaronesian flora, using the moss species complex of Rhynchostegium riparioides as a model. The deep polyphyly of R. riparioides across its distribution range reveals active differentiation that better corresponds to geographic than morphological differences. Morphometric analyses are, in fact, blurred by a size gradient that accounts for 80% of the variation observed among gametophytic traits. The lack of endemic diversification observed in R. riparioides in Macaronesia weakens the idea that the low rates of endemism observed in the Macaronesian bryophyte flora might solely be explained by taxonomic shortcomings. To the reverse, the striking polyphyly of North American and European lineages of R. riparioides suggests that the similarity between the floras of these continents has been over-emphasized. Discriminant analyses point to the existence of morphological discontinuities among the lineages resolved by the molecular phylogeny. The global rate of error associated to species identification based on morphology (0.23) indicates, however, that intergradation of shape and size characters among species in the group challenges their identification.

Phylogenetic relationships in the ‘ Pinnatella ’ clade of the moss family Neckeraceae (Bryophyta)

The family Neckeraceae is composed of three distinct clades, of which two, i.e. the Neckera and Thamnobryum clades, are well defined. The third clade, consisting of species belonging to Caduciella, Curvicladium, Handeliobryum, Himantocladium, Homaliodendron, Hydrocryphaea, Neckera, Neckeropsis, Pinnatella, Shevockia and Taiwanobryum, is the focus of this study. Based on sequence data from the trnS-rps4-trnT-trnL-trnF plastid cluster and the rpl16 intron as well as from nuclear ITS1&2, the phylogenetic relationships of these genera are reconstructed. The nearest relatives of this clade are resolved shedding more light on the evolution of the family. The generic composition of the clade and its individual genera are discussed; polyphyly requires redefinition of Pinnatella, Neckeropsis and Homaliodendron. The positions of Touwia and Homalia within the family are addressed in an additional analysis based on more extensive sequence data, and the corresponding new combinations are made. Several further taxonomic changes are proposed, including Circulifolium gen. nov., comprising the former Homaliodendron exiguum and H. microdendron.

Rhynchostegiella (Brachytheciaceae): molecular re-circumscription of a convenient taxonomic repository

Abstract The moss genus Rhynchostegiella (Helicodontioideae, Brachytheciaceae) has long served as a convenient repository for small brachythecioid pleurocarps. Its circumscription is revised in the context of a chloroplast phylogeny of the Helicodontioideae employing trnL-trnF, atpB-rbcL, psbT-psbH, and psbA-trnH sequence data. The analysis resolves with full posterior probabilities a core Rhynchostegiella clade of eight species. Rhynchostegiella pumila and R. duriaei are both resolved outside that clade and accommodated in their own genera, Microeurhynchium gen. nov. and Pseudorhynchostegiella gen. nov., respectively. Rhynchostegiella leptoneura is sister to Aerolindigia capillacea and R. papuensis is closely related to Eurhynchiella zeyheri. One of the reasons why these unrelated species, together with other taxa, were traditionally included within Rhynchostegiella, is that the genus is morphologically poorly defined by only a single synapomorphic change followed by reversals in half of the species. The Madeiran endemic Brachythecium percurrens is resolved as sister to all the other genera of the Helicodontioideae and is transferred into a new monotypic genus, Hedenasiastrum gen. nov.