Trouble with lichen: the re-evaluation and re-interpretation of thallus form and fruit body types in the molecular era

Following discussions of the definition of the terms ‘lichen’ and ‘thallus’, the role of lichenization in the evolution of asco- and basidiomycetes, and divergence and convergence in fruit body types, the morphogenetic interpretation of types of thallus form in lichens is reviewed. Attention is drawn to the various morphogenetic hypotheses proposed to explain the lichen thallus, but it is concluded that it is best interpreted as a novel phenotype with no exact homologue. Similar ascomatal and thallus types are found in lichen-forming fungi of different orders and families, as now revealed by molecular phylogenetic studies. These are interpreted as examples of convergent evolution, strategies by which unrelated fungi either display captured algae to maximize photosynthetic opportunities, or to attach themselves to a substratum. Phenotypic evolution of fruit body and thallus types in the major orders and clades is summarized, and the thallus types known in each order are tabulated. An hypothesis relating the evolution of these structures to hygroscopic movements is proposed, and the critical position of lichens in developing an integrated approach to ascomycete evolution is emphasized.     

A polysaccharide from Lichina pygmaea and L. confinis supports the recognition of Lichinomycetes

The lichen-forming order Lichinales, generally characterized by prototunicate asci and the development of thalli with cyanobacteria, has recently been recognized as a separate class of ascomycetes, Lichinomycetes, as a result of molecular phylogenetic studies. As alkali and water-soluble (F1SS) polysaccharides reflect phylogeny in other ascomycetes, a polysaccharide from Lichina pygmaea and L. confinis was purified and characterized to investigate whether these F1SS compounds in the Lichinomycetes were distinctive. Nuclear magnetic resonance (NMR) spectroscopy and chemical analyses revealed this as a galactomannan comprising a repeating unit consisting of an α-(1→6)-mannan backbone, mainly substituted by single α-galactofuranose residues at the O-2- or the O-2,4- positions linked to a small mannan core. With the exception of the trisubstituted mannopyranose residues previously described in polysaccharides from other lichens belonging to orders now placed in Lecanoromycetes, the structure of this galactomannan most closely resembles those found in several members of the Onygenales in Eurotiomycetes. Our polysaccharide data support molecular studies showing that Lichina species are remote from Lecanoromycetes as the galactofuranose residues are in the α-configuration. That the Lichinomycetes were part of an ancestral lichenized group can not be established from the present data because the extracted polysaccharide does not have the galactofuranose residue in the β configuration; however, the data does suggest that an ancestor of the Lichinomycetes contained a mannan and was part of an early radiation in the ascomycetes.     

The phylogenetic placement of Ostropales within Lecanoromycetes (Ascomycota) revisited

Results of molecular studies regarding the phylogenetic placement of the order Ostropales and related taxa within Lecanoromycetes were thus far inconclusive. Some analyses placed the order as sister to the rest of Lecanoromycetes, while others inferred a position nested within Lecanoromycetes. We assembled a data set of 101 species including sequences from nuLSU rDNA, mtSSU rDNA, and the nuclear protein-coding RPB1 for each species to examine the cause of incongruencies in previously published phylogenies. MP, minimum evolution, and Bayesian analyses were performed using the combined three-region data set and the single-gene data sets. The position of Ostropales nested in Lecanoromycetes is confirmed in all single-gene and concatenated analyses, and a placement as sister to the rest of Lecanoromycetes is significantly rejected using two independent methods of alternative topology testing. Acarosporales and related taxa (Acarosporaceae group) are basal in Lecanoromycetes. However, if the these basal taxa are excluded from the analyses, Ostropales appear to be sister to the rest of Lecanoromycetes, suggesting different ingroup rooting as the cause for deviating topologies in previously published phylogenies.     

6-MSAS-like polyketide synthase genes occur in lichenized ascomycetes

Lichenized and non-lichenized filamentous ascomycetes produce a great variety of polyketide secondary metabolites. Some polyketide synthase (PKS) genes from non-lichenized fungi have been characterized, but the function of PKS genes from lichenized species remains unknown. Phylogenetic analysis of keto synthase (KS) domains allows prediction of the presence or absence of particular domains in the PKS gene. In the current study we screened genomic DNA from lichenized fungi for the presence of non-reducing and 6-methylsalicylic acid synthase (6-MSAS)-type PKS genes. We developed new degenerate primers in the acyl transferase (AT) region to amplify a PKS fragment spanning most of the KS region, the entire linker between KS and AT, and half of the AT region. Phylogenetic analysis shows that lichenized taxa possess PKS genes of the 6-MSAS-type. The extended alignment confirms overall phylogenetic relationships between fungal non-reducing, 6-MSAS-type and bacterial type I PKS genes.     

A new species of Phaeohelotium from Nothofagus forests in Argentina and Chile, with a key to the Southern Hemisphere species

Phaeohelotium nothofagi, sp.nov., found on fallen wood and leaves of Nothofagus dombeyi, is described and illustrated. The fungus is characterized by pale yellow discs, and fumose ascospores with asperulate walls. A key with distributional data for the five species of the genus now known in the Southern Hemisphere is provided.     

Corylomyces: a new genus of Sordariales from plant debris in France

The new genus Corylomyces, isolated from the surface of a hazelnut (Corylus avellana) in the French Pyrenees, is described, illustrated and compared with morphologically similar taxa. It is characterised by tomentose, ostiolate ascomata possessing long necks composed of erect to sinuose hairs, and one- or two-celled, opaque, lunate to reniform ascospores. Analyses of the SSU and LSU fragments rDNA gene sequences support its placement in the Lasiosphaeriaceae (Sordariales).     

Hypocrella panamensis sp. nov. (Clavicipitaceae, Hypocreales): a new species infecting scale insects on Piper carrilloanum in Panama

A new species, Hypocrella panamensis, is described from collections and cultures obtained on Barro Colorado Island, Panama. In order to aid in placement of this fungus, phylogenetic analyses were conducted using LSU (rDNA) sequences. Hypocrella panamensis is characterized by possessing pulvinate stromata with a Lecanicillium-like anamorphic state and superficial perithecia. Hypocrella panamensis consistently grouped in a clade containing Hypocrella nectrioides, H. phyllogena, and H. africana (100 % PP). Most species of Hypocrella possess Aschersonia or Hirsutella anamorphs. Hypocrella panamensis is unique in the genus Hypocrella in possession of a Lecanicillium-like anamorphic state. In its biological habit Hypocrella panamensis is similar to other species in Hypocrella in that it infects and degrades the scale insect, then grows superficially on nutrients that emerge to the plant surface through the stylet wound.     

Morphology and development of Nigrosabulum globosum, a cleistothecial coprophile in the Bionectriaceae (Hypocreales)

Recent DNA sequence analyses indicated that Nigrosabulum globosum is a cleistothecial representative of the Bionectriaceae in the Hypocreales, but morphological characters supporting this relationship are unknown. Using light and electron microscopy we followed the development of the ascomata of this species, from the formation of gametangia through to the development of mature ascospores, and observed a series of characters that confirmed its hypocrealean affinities. These included the formation of a gel-filled centrum during early stages of ascoma development, the subsequent appearance of hyaline peridial tissue enclosed within a layer we interpret as representing a melanized uniloculate stroma, apically derived paraphyses, and an ascogenous system that gives rise to asci that were both cylindrical to clavate and globose. Ascospores, previously reported to be smooth, were ornamented with a honeycomb-like reticulum and were able to germinate within the ascoma. The carbonaceous outer (stromatic) walls of the mature, grit-like cleistothecia indicate possible resistance to UV radiation and desiccation. Furthermore, the complement of germinated ascospores would enable mature ascomata to function as propagules that could quickly initiate new growth when transferred to fresh substrate. Our reexamination of N. globosum also provides data that support the hypothesized close relationship with other bionectriaceous, cleistothecial coprophiles, i.e., species of Hapsidospora, and Bulbithecium in particular.     

Development and dehiscence of the cephalothecoid peridium in Aporothielavia leptoderma shows it belongs in Chaetomidium

The development of the cephalothecoid peridium of Aporothielavia leptoderma was examined using light and electron microscopy. Early stages in ascoma initiation were consistent with previous reports for other species in the Chaetomiaceae. However, as young cleistothecia increased in size, clusters of peridial cells in the outer textura angularis elongated in a radial pattern around a central cell or cell cluster to form rosettes of relatively thick-walled segments that marked the central areas of incipient cephalothecoid plates. The external flank along median portions of the radial cells became thin walled and swelled outwards so that each plate became concave and was separated from adjacent plates by a more or less circular to polygonal ridge of knuckle-shaped swellings. When dry, mature peridia split apart along some of the ridges demarcating individual plates but an internal mechanism for liberating ascospores from the confines of the ascoma was not observed. Physical disturbance of mature cleistothecia by beetles, when enclosed together in a Petri dish, shattered the peridia, liberating the ascospores. Smaller insects were unable to cause disarticulation of the cephalothecoid plates. Because of the presence of an apical germ pore in the ascospores and morphological similarity to Chaetomidium arxii, the new combination Chaetomidium leptoderma (syn. Thielavia leptoderma) comb. nov. is proposed.     

A reassessment of cleistothecia as a taxonomic character

The morphology of sexual fruit bodies has been historically regarded as a key character in fungal taxonomy. In the 1970s the class Plectomycetes was recognized in order to classify the cleistothecial ascomycetes. However, recent analysis of DNA sequencing data concerning the phylogeny of numerous cleistothecial ascomycetes confirmed that the criterion of the production of closed ascomata without a predefined opening and with an irregular arrangement of the asci at the centrum is of little systematic value, as pointed out by different authors on the basis of morphological studies.     

Chaetosphaeria tortuosa, the newly discovered teleomorph of Menispora tortuosa, with a key to known Menispora species

Chaetosphaeria tortuosa is described as the newly discovered teleomorph of Menispora tortuosa, based on specimens from Canada and the Czech Republic, and single spore isolations from both morphs. The fungus produces superficial, more or less globose, papillate, dark brown to black smooth perithecia (200–)220–250 × (220–)230–260 μm. The asci are unitunicate, 8-spored, cylindrical-fusiform, (110–)120–133(–145) × 12–14 with a distinct apical, nonamyloid annulus 1–1.5 μm high, 3.5–4 μm wide. The ascospores are fusiform, 19–24 × 5–6 μm, hyaline, 3-septate, smooth, and 2-seriate in the ascus. The morphology of the teleomorph and anamorph are similar to that of C. ovoidea (anamorph: M. glauca), differing in dimensions of asci and ascospores, and in the disposition and morphology of the phialides of the anamorphs. The generic concept and phylogeny of Menispora is briefly discussed, and a key to the 11 species currently accepted in the genus is provided.