Photobiont Layer Research Articles

Acquisition of green algal photobionts enables both chlorolichens and chloro-cyanolichens to activate photosynthesis at low humidity without liquid water.

Cyanobacteria require liquid water for photosynthesis, whereas green algae can photosynthesise with water vapour alone. We discovered that several Lobaria spp. which normally have cyanobacteria as the sole photobiont, in some regions of the trans-Himalayas also harboured green algae. We tested whether green algal acquisition was: limited to high elevations; obtained from neighbouring chloro-Lobaria species; enabled photosynthesis at low humidity. Lobaria spp. were collected from 2000 to 4000 m elevation. Spectrophotometry quantified green algal abundance by measuring chlorophyll b (absent in cyanobacteria). Thalli cross-sections visually confirmed green algal presence. We sequenced gene regions: Lobaria (ITS-EF-1α-RPB2), green algae (18S-RBC-L) and Nostoc (16S). Phylogenetic analysis determined myco-photobiont associations. We used a custom closed-circuit gas exchange system with an infrared gas analyser to measure CO2 exchange rates for desiccated specimens at 33%, 76%, 86% and 98% humidity. Cross-sections revealed that the photobiont layers in putative cyano-Lobaria contained both cyanobacteria and green algae, indicating that they should be considered chloro-cyanolichens. Chloro-Lobaria had no visible cephalodia nor cyanobacteria in the photobiont layer. Chloro-Lobaria and chloro-cyano-Lobaria had comparable levels of chlorophyll b. Chloro-Lobaria usually contained Symbiochloris. Chloro-cyano-Lobaria mainly associated with Parachloroidium and Nostoc; infrequently with Symbiochloris, Apatococcus, Chloroidium, Pseudochlorella, Trebouxia. Sequences from two green algal genera were obtained from within some thalli. Desiccated specimens of every Lobaria species could attain net photosynthesis with light exposure and 33% humidity. CO2 exchange dynamics over a five-day period differed between species. At all elevations, chloro-cyano-Lobaria spp. had abundant green algae in the photobiont layer, but green algal strains mostly differed to those of chloro-Lobaria spp. Both chloro-Lobaria and chloro-cyano-Lobaria were capable of conducting photosynthesis without liquid water. The data strongly suggest that they attained positive net photosynthesis.

Alcobiosis, an algal-fungal association on the threshold of lichenisation

Alcobiosis, the symbiosis of algae and corticioid fungi, frequently occurs on bark and wood. Algae form a layer in or below fungal basidiomata reminiscent of the photobiont layer in lichens. Identities of algal and fungal partners were confirmed by DNA barcoding. Algal activity was examined using gas exchange and chlorophyll fluorescence techniques. Carbon transfer from algae to fungi was detected as 13C, assimilated by algae, transferred to the fungal polyol. Nine fungal partners scattered across Agaricomycetes are associated with three algae from Trebouxiophycae: Coccomyxa sp. with seven fungal species on damp wood, Desmococcus olivaceus and Tritostichococcus coniocybes, both with a single species on bark and rain-sheltered wood, respectively. The fungal partner does not cause any obvious harm to the algae. Algae enclosed in fungal tissue exhibited a substantial CO2 uptake, but carbon transfer to fungal tissues was only detected in the Lyomyces-Desmococcus alcobiosis where some algal cells are tightly enclosed by hyphae in goniocyst-like structures. Unlike lichen mycobionts, fungi in alcobioses are not nutritionally dependent on the algal partner as all of them can live without algae. We consider alcobioses to be symbioses in various stages of co-evolution, but still quite different from true lichens.

Eight new species of lichenized Basidiomycota in the genera Acantholichen, Cyphellostereum and Dictyonema s.str. (Agaricales, Hygrophoraceae) from northern South America

A study of Acantholichen P.M. Jørgensen, Cyphellostereum D.A. Reid and Dictyonema s.str. C. Agardh ex Kunth from the Venezuelan Andes (Sierra Nevada de Mérida) and the Guayana Highlands (Alto Orinoco) revealed the presence of eight species new to science, viz., Acantholichen dendroideus V. Marcano, Cyphellostereum mucuyense V. Marcano, Dictyonema andinum V. Marcano, D. duidense V. Marcano, D. laurae V. Marcano, D. subinvolutum V. Marcano, D. subsericeum V. Marcano and D. umbricola V. Marcano. Acantholichen dendroideus grows on mosses in shady and humid disturbed forest and is characterized by densely and dichotomously branched microsquamules, with a pruinose surface and large acanthohyphidia. Cyphellostereum mucuyense grows on mosses and sandy soils, lacks a jigsaw-puzzle-shaped hyphal sheath and prothallus, the fibrils are not penetrated by tubular fungal hyphae and the basidiocarp surface is finely arachnoid. This is the first record of Cyphellostereum in Venezuela. Dictyonema andinum might be confused with D. irrigatum (Berkeley & M. A. Curtis) Lücking from the Andaman Islands, but differs in the broader and ascending fibrils, a thicker photobiont layer and hypothallus, as well as the formation of stereoid-corticioid hymenophores. Dictyonema duidense from the Guayana Highlands and D. subsericeum from the Venezuelan Andes belong in the group of shelf-like morphotypes, with a semicircular thallus resembling D. sericeum s.str. Dictyonema duidense grows on tree trunks and is characterized by thick, very broad lobes and an areolate, rugose surface and it lacks clamp connections whereas D. subsericeum grows on tree branches and is characterized by variability of color (white, greenish blue, brown), size and shape (semicircular to hemispherical), filamentous lobes, a hirsute surface, fibrillose margins, clamp connections on the hyphae, cyphelloid hymenophores resembling attachment hapters, and very small, globose to subglobose basidiospores. Dictyonema laurae resembles D. subsericeum but is characterized by a continuous greenish blue crust-like thallus with an irregular surface, with discontinuous, fibrillose, and narrow margins projecting and ascending from the substrate, a hapteriform hymenophore, and its lacks clamp connections on the hyphae. Dictyonema subinvolutum is characterized by a jigsaw-puzzle-shaped hyphal sheath, fibrils penetrated by tubular fungal hyphae, and a smooth, pruinose, resupinate hymenophore. Finally, D. umbricola grows on mosses in very shady habitats and produces a corticioid hymenophore raised from the thallus, resembling apothecial discs, jigsaw-puzzle-shaped cells around the filaments and a distinct, discontinuous, white prothallus. Of the eight species of Dictyonema s.lat. registered from Venezuela, seven are known only from the Venezuelan Andes (A. dendroideus, C. mucuyense, D. andinum, D. laurae, D. subsericeum, D. subinvolutum, D. umbricola) and one is known only from the Venezuelan Amazonas (D. duidense). The high concentration of Acantholichen, Cyphellostereum and Dictyonema species in tropical America and especially of the latter genus in the Venezuelan Andes indicates that this region constitutes an important centre for speciation and endemism of Dictyonema clade/subtribe Dictyonematinae.

Melanisation in Boreal Lichens Is Accompanied by Variable Changes in Non-Photochemical Quenching.

Lichens often grow in microhabitats where they absorb more light than they can use for fixing carbon, and this excess energy can cause the formation of harmful reactive oxygen species (ROS). Lichen mycobionts can reduce ROS formation by synthesizing light-screening pigments such as melanins in the upper cortex, while the photobionts can dissipate excess energy radiationlessly using non-photochemical quenching (NPQ). An inherent problem with using fluorimetry techniques to compare NPQ in pale and melanised thalli is that NPQ is normally measured through a variously pigmented upper cortex. Here we used a dissection technique to remove the lower cortices and medullas of Lobaria pulmonaria and Crocodia aurata and then measure NPQ from the underside of the thallus. Results confirmed that NPQ can be satisfactorily assessed with a standard fluorimeter by taking measurement from above using intact thalli. However, photobionts from the bottom of the photobiont layer tend to have slightly lower rates of PSII activity and lower NPQ than those at the top, i.e., display mild “shade” characteristics. Analysis of pale and melanised thalli of other species indicates that NPQ in melanised thalli can be higher, similar or lower than pale thalli, probably depending on the light history of the microhabitat and presence of other tolerance mechanisms.

Lichens Bite the Dust - A Bioweathering Scenario in the Atacama Desert.

SummaryBioweathering mediated by microorganisms plays a significant role in biogeochemical cycles on global scales over geological timescales. Single processes induced by specific taxa have been described but could rarely be demonstrated for complex communities that dominate whole landscapes. The recently discovered grit crust of the coastal Atacama Desert, which is a transitional community between a cryptogamic ground cover and a rock-bound lithic assemblage, offers the unique chance to elucidate various bioweathering processes that occur simultaneously. Here, we present a bioweathering scenario of this biocenosis including processes such as penetration of the lithomatrix, microbial responses to wet-dry cycles, alkalinolysis, enzyme activity, and mineral re-localization. Frequently occurring fog, for example, led to a volume increase of microorganisms and the lithomatrix. This, together with pH shifts and dust accumulation, consequently results in biophysical breakdown and the formation of a terrestrial protopedon, an initial stage of pedogenesis fueled by the grit crust.

Melanic pigments and canopy-specific elemental concentration shape growth rates of the lichen Lobaria pulmonaria in unmanaged mixed forest

How do elemental composition (published data) and melanin (new data) shape the relative growth rate (RGR; new data) of the cephalolichen Lobaria pulmonaria, a member of the Lobarion community? We transplanted L.pulmonaria onto Picea glauca x engelmannii branches in three unmanaged canopy settings in inland British Columbia: within Populus dripzones supporting Lobarion; outside dripzones supporting Lobarion; and outside dripzones without Lobarion (non-Lobarion). A year later, lichen RGR was highest in the Lobarion, intermediate in the dripzone, and lowest in the non-Lobarion). RGR increased with Ca- and P-concentration, but declined with Zn, S, initial level of melaninic pigmentation, tree height, and elevation. Bark pH lost significance in multiple regression models when lichen elemental concentrations were included. Along canopy openness gradients, acclimation by the solar radiation-induced melanin had compensated for varying light. By the end of the experiment, melanin thus did not affect RGR probably because it normalized the light in the photobiont layer across sites.

Reprint of Efficient fungal UV-screening provides a remarkably high UV-B tolerance of photosystem II in lichen photobionts

Lichen photobionts in situ have an extremely UV-B tolerant photosystem II efficiency (Fv/Fm). We have quantified the UV-B-screening offered by the mycobiont and the photobiont separately. The foliose lichens Nephroma arcticum and Umbilicaria spodochroa with 1: intact or 2: removed cortices were exposed to 0.7 Wm-2 UV-BBE for 4 h. Intact thalli experienced no reduction in Fv/Fm, whereas cortex removal lowered Fv/Fm in exposed photobiont layers by 22% for U. spodochroa and by 14% for N. arcticum. We also gave this UV-B dose to algal cultures of Coccomyxa and Trebouxia, the photobiont genera of N. arcticum and U. spodochroa, respectively. UV-B caused a 56% reduction in Fv/Fm for Coccomyxa, and as much as 98% in Trebouxia. The fluorescence excitation ratio (FER) technique comparing the fluorescence from UV-B or UV-A-excitation light with blue green excitation light using a Xe-PAM fluorometer showed that these photobiont genera did not screen any UV-B or UV-A The FER technique with a Multiplex fluorometer estimated the UV-A screening of isolated algae to be 13–16%, whereas intact lichens screened 92–95% of the UV-A. In conclusion, the cortex of N. arcticum and U. spodochroa transmitted no UV-B and little UV-A to the photobiont layer beneath. Thereby, the upper lichen cortex forms an efficient fungal solar radiation screen providing a high UV-B tolerance for studied photobionts in situ. By contrast, isolated photobionts have no UV-B screening and thus depend on their fungal partners in nature.

Efficient fungal UV-screening provides a remarkably high UV-B tolerance of photosystem II in lichen photobionts

Lichen photobionts in situ have an extremely UV-B tolerant photosystem II efficiency (Fv/Fm). We have quantified the UV-B-screening offered by the mycobiont and the photobiont separately. The foliose lichens Nephroma arcticum and Umbilicaria spodochroa with 1: intact or 2: removed cortices were exposed to 0.7 Wm-2 UV-BBE for 4 h. Intact thalli experienced no reduction in Fv/Fm, whereas cortex removal lowered Fv/Fm in exposed photobiont layers by 22% for U. spodochroa and by 14% for N. arcticum. We also gave this UV-B dose to algal cultures of Coccomyxa and Trebouxia, the photobiont genera of N. arcticum and U. spodochroa, respectively. UV-B caused a 56% reduction in Fv/Fm for Coccomyxa, and as much as 98% in Trebouxia. The fluorescence excitation ratio (FER) technique comparing the fluorescence from UV-B or UV-A-excitation light with blue green excitation light using a Xe-PAM fluorometer showed that these photobiont genera did not screen any UV-B or UV-A The FER technique with a Multiplex fluorometer estimated the UV-A screening of isolated algae to be 13–16%, whereas intact lichens screened 92–95% of the UV-A. In conclusion, the cortex of N. arcticum and U. spodochroa transmitted no UV-B and little UV-A to the photobiont layer beneath. Thereby, the upper lichen cortex forms an efficient fungal solar radiation screen providing a high UV-B tolerance for studied photobionts in situ. By contrast, isolated photobionts have no UV-B screening and thus depend on their fungal partners in nature.

Short-term influence of Cu, Zn, Ni and Cd excess on metabolism, ultrastructure and distribution of elements in lichen Xanthoria parietina (L.) Th. Fr.

Lichens are symbiotic organisms that are very sensitive to heavy metal pollution. However, there is little evidence of how heavy metal pollution affects the physiological status, ultrastructural changes and distribution of elements in the layers of lichen thalli. For this purpose we simulated metal pollution to lichens and studied its impact on Xanthoria parietina. Thalli were treated with the heavy metals Cu, Zn, Ni, Cd in the form of sulfates at concentrations of 100µM and 500µM during 24, 48 and 72h. Untreated lichens served as controls. We assessed the status of physiological parameters (fluorescence and integrity of chlorophyll a, content of soluble proteins and ergosterol), ultrastructural changes, especially to the photobiont, and the distribution of elements in the layers of thalli in relation to treatment with heavy metals. We found positive correlations between the content of all tested heavy metals and the physiological response. We assessed the toxicity of the selected metals as follows: Cd >= Cu >= Ni > Zn, based on the effects on the photobiont layer in the lichen thallus and physiological measurements.

The influence of structural organization of epilithic and endolithic lichens on limestone weathering

AbstractHyphal penetration, mineral dissolution and neoformation at the lichen–rock interface have been widely characterized by microscopic and spectroscopic studies, and considered as proxies of lichen deterioration of stone substrates. However, these phenomena have not been clearly related to experimental data on physical properties related to stone durability, and the physical consequences of lichen removal from stone surfaces have also been overlooked. In this study, we combine microscopic and spectroscopic characterization of the structural organization of epi‐ and endolithic lichens (Caloplaca marina (Wedd.) Du Rietz, Caloplaca ochracea (Schaer.) Flagey, Bagliettoa baldensis (A.Massal.) Vězda, Porina linearis (Leight.) Zahlbr., Verrucaria nigrescens Pers.) at the interface with limestones of interest for Cultural Heritage (Portland Limestone, Botticino Limestone), with analysis of rock properties (water absorption, surface hardness) relevant for durability, before and after the removal or scraping of lichen thalli. Observations using reflected‐light and electron microscopy, and Raman analyses, showed lichen–limestone stratified interfaces, differing in the presence/absence and depth of lichen anatomical layers (lithocortex, photobiont layer, pervasive and sparse hyphal penetration component) depending on species and lithology. Specific structural organizations of lichen–rock interface were found to be associated with differential patterns of water absorption increase, evaluated by Karsten tube, in comparison with surfaces with microbial biofilms only, even more pronounced after the removal or scraping of the upper structural layers. Equotip measurements on surfaces bearing intact thalli showed lower hardness in comparison with control surfaces. By contrast, after the removal or scraping procedures, Equotip values were similar to or higher than those of controls, suggesting that the increasing open porosity may be related to a biogenic hardening process. Such counterposed patterns of porosity increase and hardening need to be considered when models relating lichen occurrence on limestones and biogeomorphological surface evolution are proposed, and to evaluate the consequences of lichen removal from stone‐built cultural heritage. Copyright © 2017 John Wiley & Sons, Ltd.

A world key to Cryptothecia and Myriostigma (Arthoniaceae), with new species and new records from the Andaman and Nicobar Islands, India

A world key to the genera Cryptothecia and Myriostigma is presented. Four species of Cryptothecia: C. albomaculans, C. elata, C. elongata and C. superphyllinica, and a Myriostigma: M. nicobaricum are described as new to science from the Andaman and Nicobar Islands, India. Cryptothecia albomaculans has a heteromerous thallus, whitish ascigerous areas not elevated above the thallus, ellipsoid, 9–11 × 3–5 septate ascospores of 47–57 × 24–30 µm and produces 2’-O-methylperlatolic acid. Cryptothecia elata has a homoiomerous thallus with distinctly raised ascomata, ascospores of (72–)84–122 × (25–)36–62(–72) µm and contains 2’-O-methylmicrophyllinic acid. Cryptothecia elongata has a heteromerous thallus, raised, irregular, 1–4 mm wide ascigerous areas covered by a photobiont layer, narrowly ellipsoid-oblong, 16–24 × 2–6 septate ascospores of 90–114 × 21–30 µm, and produces gyrophoric and lecanoric acids. Cryptothecia superphyllinica has a homoiomerous thallus, whitish, raised, rounded to linear ascigerous areas 0.5–1.5 mm in diam., broadly ovoid to ellipsoid, 9–15 × 3–6 septate ascospores of (45–)58–76(–80) × (22–)24–33(–38) µm and 2’-O-methylsuperphyllinic acid. Myriostigma nicobaricum has a homoiomerous thallus, whitish, raised, rounded, ascigerous areas 0.3–0.8 mm in diam., broadly ellipsoid to ovoid, 8–11 × 2–4 septate, 34–48 × 16–22 µm ascospores and confluentic acid. Cryptothecia aleurodes, C. eungellae and C. striata are new additions to the lichen biota of India. Ascospores of Cryptothecia eungellae are described for the first time and illustrated.

New species ofDictyonemaandCyphellostereum(lichenizedBasidiomycota:Hygrophoraceae) from tropical Africa and the Indian Ocean, dedicated to the late Hildur Krog

Abstract: A small collection of lichenized fungi belonging in the Dictyonema clade from E Africa and Mauritius, tentatively identified as D. sericeum, revealed four species new to science, one in the genus Cyphellostereum and three in the genus Dictyonema s.str. Cyphellostereum bicolor from Mauritius is similar to C. imperfectum from Guatemata, but differs in the absence of a persistent white hypothallus and the less compact hyphal sheath of the fibrils, as well as the formation of resupinate hymenophores. Dictyonema album, also from Mauritius, belongs in the group of shelf-like morphotypes and is characterized within this group by very loose tufts dominated by sterile hyphae with very loosely arranged cyanobacterial fibrils. Dictyonema krogiae from Kenya is another new species in the group with shelf-like thalli and is the first species in this group known to form a distinctly layered thallus, with very compact photobiont layer, loose medulla, and more compact lower cortex. Finally, Dictyonema tricolor f...

Lichen preservation in amber: morphology, ultrastructure, chemofossils, and taphonomic alteration

Abstract. The fossil record of lichens is scarce and many putative fossil lichens do not show an actual physiological relationship between mycobionts and photobionts or a typical habit, and are therefore disputed. Amber has preserved a huge variety of organisms in microscopic fidelity, and so the study of amber fossils is promising for elucidating the fossil history of lichens. However, so far it has not been tested as to how amber inclusions of lichens are preserved regarding their internal characters, ultrastructure, and chemofossils. Here, we apply light microscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and Raman spectroscopy to an amber-preserved Eocene lichen in order to gain information about the preservation of the fossil. The lichen thallus displays lifelike tissue preservation including the upper and lower cortex, medulla, photobiont layer, apothecia, and soredia. SEM analysis revealed globular photobiont cells in contact with the fungal hyphae, as well as impressions of possible former crystals of lichen compounds. EDX analysis permitted the differentiation between halite and pyrite crystals inside the lichen which were likely formed during the later diagenesis of the amber piece. Raman spectroscopy revealed the preservation of organic compounds and a difference between the composition of the cortex and the medulla of the fossil.

Relationship between the algal partners and the growth of lichen-forming fungus Porpidia crustulata

In recent years, examinations based on morphological characters and phylogenetic analyses have begun to reveal the diversity of photobionts in lichen symbioses. However, still little is known regarding genetic diversity and ecological adaptation of algal partners in lichen symbioses. In this study, we investigated the photobiont Chlorella “sp. GC” (Trebouxiophyceae), a partner of Porpidia crustulata from the Guancen Mountains, China. We examined the relationship between photobiont layer thickness and Porpidia crustulata growth over a 6-year period (2007–2012). Although Porpidia crustulata exhibited moderate growth rates (0.4–0.62 mm year−1), photobiont layer became increasingly thinner over the six-year period. We speculate that prolonged exposure to sunlight and desiccation may deleteriously alter photobiont morphology and physiology. Porpidia crustulata may be forced into a state of physiological dormancy.

Bacterial epibionts and endolichenic actinobacteria and fungi in the Lower Devonian lichen Chlorolichenomycites salopensis

The charcoalified fragment of the dorsiventrally organized, internally stratified presumed green algal lichen Chlorolichenomycites salopensis from the Lower Devonian Lochkovian strata in the Welsh Borderland carries bacterial colonies on the upper surface, i.e. the cortex, and actinobacterial filaments in the medulla underneath the photobiont layer. Moreover relatively thin hyphae of presumed endolichenic fungi were found. As in extant lichens, which are best regarded as consortia with an unknown number of participants, this internally stratified, fossil thallus fragment of a presumed green algal lichen harbours a diverse microbial community.

Arthopyrenia betulicola (Arthopyreniaceae, Dothidiomycetes), an Unusual New Lichenized Fungus From High Elevations of the Southern Appalachian Mountains

The crustose pyrenolichen Arthopyrenia betulicola is described as new to science based on collections from high elevations of Great Smoky Mountains National Park in eastern North America. The species is hypothesized to be endemic to the southern Appalachian Mountains where it occurs only on the bark of mature yellow birch (Betula alleghaniensis). It is a somewhat unusual member of the genus Arthopyrenia s.l. in consistently having a conspicuous photobiont layer of Trentepohlia. It differs from A. cinchonae, with which it is allopatric, by this feature as well as in having differently shaped and narrower ascospores.

Interspecific and intraspecific variations in water storage in epiphytic old forest foliose lichens

Cyanolichens ( Lobaria hallii , Lobaria retigera , Lobaria scrobiculata , Pseudocyphellaria anomala ) and cephalodial ( Lobaria pulmonaria ) and noncephalodial ( Platismatia glauca ) chlorolichens were sampled in dry open, mesic open, and mesic closed forests in central British Columbia. Specific thallus mass (STM), water-holding capacity (WHC), percent water content at saturation, and thickness of upper cortex, photobiont layer, and medulla plus lower cortex were measured. Whereas STM did not differ much between cyanolichens (9.8 ± 0.1 mg dry mass·cm–2) and chlorolichens (8.0 ± 0.1 mg dry mass·cm–2), cyanolichens had a WHC (20.3 ± 0.2 mg H2O·cm–2) that was nearly twice that of the chlorolichens (10.8 ± 0.2 mg H2O·cm–2). STM and WHC increased with light exposure at the studied sites, presumably as an acclimation to higher evaporation demands. Within species, WHC was strongly coupled to STM and increased substantially faster with STM in cyanolichens, compensating their inability to use humid air to restore photosynthesis. The photobiont layer was two times thicker in cyanolichens, whereas the thickest layer (the hydrophobic medulla) did not differ between cyanolichens and chlorolichens. Most interspecific variation (88.3%) in WHC could be accounted for in a multiple regression model where STM and photobiont to total thickness ratio were the most important independent variables. Photobionts thus play significant roles in the water economy of lichens.

A first assessment of Galapagos basidiolichens

As part of an ongoing comprehensive inventory of Galapagos lichens, a first assessment of the morphology and anatomy of basidiolichens from the archipelago is presented here. It is the basis for further studies of the taxonomy, ecology and biogeography of this poorly known group of lichens. Four genera, all in Hygrophoraceae, can be distinguished: Acantholichen, Cora, Cyphellostereum and Dictyonema. Both Acantholichen and Cora are characterized by chroococcoid cyanobionts and a heteromerous thallus with a distinct upper cortex and photobiont layer. The monotypic Acantholichen pannarioides is entirely composed of small, branched, inflated squamules that appear densely pruinose because their cortical hyphae bear characteristically swollen, densely spinose end cells (acanthohyphidia); this species has never been observed fertile. The common Cora glabrata is foliose, forming large, radially zonate, conch-like, often tiled thalli, when fertile with circular lines of basidiocarps on its lower side. Dictyonema is distinguished by filamentous cyanobionts and distinctly filamentous thalli that are homomereous (i.e., not distinctly layered); all species of Dictyonema s.str. have trichomes (filamentose cyanobacterial photobionts) closely enveloped by fungal cells of a jigsaw pattern. In D. sericeum thallus filaments (i.e., individual fibrils) aggregate to form shelf-like structures similar in appearance to polyporoid bracket fungi; basidiocarps develop in irregular patches on the lower side of these shelves. In contrast, fibrils of D. schenkianum grow encrusting their substrate with irregularly to suberect trichomes, occasionally bearing basidiocarps dispersed across the thallus. Two other species in Galapagos show adpressed growth form and are described here as new: Dictyonema pectinatum, which is characterized by large parallel fibrils with paler, papillate tips, and D. galapagoense, characterized by thin trichomes of more squarrish elongate cells. The genus Cyphellostereum is represented by two species: the newly described C. imperfectum and an unnamed Cyphellostereum sp., both phenotypically similar to free-living cyanobacterial filaments. Cyphellostereum imperfectum has narrow photobiont filaments with irregular hyphal sheath leaving interspaces; macroscopically it shows a bluish green thallus with a distinct prothallus. Cyphellostereum sp. has a rather uncommon basidiolichen appearance: thin sctytonematoid fibrils surrounded by straight fungal cells forming shiny tufts. The new combination Cyphellostereum nitidum is also proposed. The ecology and taxonomy of Galapagos basidiolichens is briefly discussed and a key and short descriptions of all species are presented.

Snails avoid the medulla of Lobaria pulmonaria and L. scrobiculata due to presence of secondary compounds

Abstract Lichens are frequently grazed by various invertebrates, such as snails and slugs. However, these gastropods discriminate between the various layers of the lichen thallus. Likewise, carbon based secondary compounds (CBSCs), some of which are known to deter lichenivores, are unevenly distributed between the various layers. In this study, the degree of rejection of medullary CBSCs by gastropods is investigated. The snail Cochlodina laminata was offered the lichens Lobaria pulmonaria and L. scrobiculata with and without CBSCs. The secondary compounds were removed by rinsing dry thalli in acetone. The snails completely avoided the medulla of thalli with natural levels of CBSCs. However, they grazed through all layers perpendicularly after these compounds had been removed. Hence, the medullary compounds restrict feeding by gastropods to the cortical and sometimes also the photobiont layer.

UV-B induces cell death in the lichen Physcia semipinnata (J.F.Gmel)

We have examined the consequences of Ultraviolet-B (UV-B) irradiation in the thallus of the lichen Physcia semipinnata (J.F.Gmel) in terms of cell viability and apoptotic-like formation. UV-B induced oligonucleosomal DNA fragmentation was detected by TUNEL assay and this is the first study showing DNA fragmentation in thalli. The intensity of TUNEL-positive cells after exposure to UV-B at doses up to 95.9 J/cm2 was higher in the photobiont layer than the mycobiont layer.